Patent Publication Number: US-2023157939-A1

Title: Personal care compositions with enhanced solubility actives

Description:
FIELD OF THE INVENTION 
     The invention relates to topical personal care compositions containing active skin benefit agents which increase glutathione production within skin cells. The solubility of the skin benefit agents is enhanced in the compositions. 
     BACKGROUND OF THE INVENTION 
     Glutathione (GSH) is the main antioxidant in all the body tissues of mammals. As an antioxidant, GSH protects cells from oxidation by quenching reactive oxygen species. GSH is believed to play a significant role in protecting cells against the cytotoxic effects of ionizing radiation, heat, certain chemicals, and solar UV radiation. While true in all areas of the body, this is particularly important in the skin, which is exposed to damaging effects of radiation, particularly UV radiation, and environmental pollutants. Decrease in the intracellular concentration of glutathione in skin is associated with cell damage, inflammation, skin darkening, discoloration, spots or freckles caused by exposure to ultraviolet radiation, and overall physiological aging. GSH is a tripeptide that consists of glutamate, cysteine, and glycine. 
     Compositions for potentiating intracellular glutathione production have been described. See e.g. Chiba et al. U.S. Pat. No. 7,740,831, Crum et al (USRE37934, USRE42645, WO2016/033183, and US20050271726); Mammone U.S. Pat. No. 6,149,925, and Perricone US 20060063718. Topical compositions and enhanced generation of glutathione in skin from its constituent amino acids (glutamate, cysteine, and/or glycine, i.e., glutathione precursors) for cellular uptake and synthesis of the GSH tripeptide were addressed in, e.g., Applicant&#39;s U.S. Published Patent Application Nos.: US2020/9034, US2020/16059, and US2019/328631. 
     The quantity of glutathione in cells depends to a large degree on the availability of cysteine in the cells. Cysteine may increase cellular levels of GSH, but the exposed sulfhydryl group of cysteine renders it unstable and reactive. Cysteine also causes strong unpleasant odor, which is an unacceptable feature of topical cosmetic products. Unlike cysteine, cystine can be administered safely; cystine is transported into the cell and converted to cysteine within the cell, the cysteine then being available for intracellular GSH production. 
     Delivery of cystine from topical compositions, however, is challenging due to its extremely low solubility in biologically acceptable vehicle in a neutral pH range, which is the pH range required for topical application. The solubility of cystine in water is 0.112 mg/ml at 25° C.; cystine is more soluble in aqueous solutions with pH less than 2 or pH above 8. The solubility of cystine in water is low as it tends to crystallize out of solution. N-acetyl-L-cysteine (“NACys”) inhibition of cystine crystal growth is disclosed in Cryst. Eng. Comm, 2016, 18, 8587. 
     A number of cysteine/cystine derivatives, including p-substituted cysteine/cystines, cystine diamides, cystine dialkyl esters and N-alkanoylcysteines have been described in connection with organ benefits for kidneys (See for instance, Zhu, et al., “Rational Design of Novel Crystal Growth Inhibitors for Treatment of Cystinuria Kidney Stones,” 2013  ProQuest Dissertations and Theses ; and CrystEngComm, 2016, 18, 8587). According to Zhu, et al., N,N′-diacetyl-L-cystine (“NDAC”) was not effective as an inhibitor of cystine crystal growth. 
     Furthermore, skin cosmetic or personal care compositions using NDAC and/or NDAC salt have not been found. 
     The present invention is based in part on a surprising finding that unique combinations of cystine with N,N′-diacetyl-L-Cystine (“NDAC”) counter-act the drawback of cystine&#39;s low solubility at neutral pH. Furthermore, by virtue of including the NDAC, more cystine can be solubilized, which, when topically applied, may increase intracellular production of glutathione. Additionally, proteases in the body can cleave (or hydrolyze) the N-acetyl bonds of NDAC to ultimately generate cystine, thus, NDAC can also serve as a controlled release alternate source of cystine. 
     SUMMARY OF THE INVENTION 
     The invention provides a topical personal care composition according to claim  1 . 
     In one embodiment, the topical cosmetic skin composition is a leave-on composition, especially a leave-on non-solid composition. 
     In one embodiment, the present invention provides a method of improving skin appearance, comprising applying the personal care composition to the skin. 
     In one embodiment, the present invention provides a method of attaining even skin color and reducing pigmentation, age spots and discoloration, comprising applying the composition to skin. 
     A preferred method of obtaining the benefits of the composition is via regular/chronic topical application of the composition, to prevent development of skin damage which may result from even routine exposure to UV light or other environmental insults which generate reactive oxygen species (“ROS”). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. 
     The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention. In addition, each of the examples given in connection with the various embodiments of the invention which are intended to be illustrative, and not restrictive. 
     Except in the examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word “about.” All amounts are by weight of the final composition, unless otherwise specified. 
     The disclosure of the invention as found herein is to be considered to cover all embodiments found in the claims as being multiply dependent upon each other, irrespective of the fact that claims may be found without multiple dependency or redundancy. In specifying any range of concentration or amount, any particular upper concentration can be associated with any particular lower concentration or amount. 
     “Comprising” is intended to mean “including” but not necessarily “consisting of” or “composed of.” In other words, the listed steps or options need not be exhaustive. 
     “Skin” is meant to include skin on the face, neck, chest, back, arms (including underarms), hands, legs, buttocks and scalp. 
     “Leave-on composition” refers to a composition that is applied to the skin and is not intended to be washed or rinsed off for some period of time, specifically hours, as contrasted with skin cleansing or wash-off or rinse-off compositions which are rinsed off or washed off immediately or minutes after the application. 
     “Non-solid” with respect to the composition means that the composition has a measurable viscosity (measurable for instance with a Brookfield Viscometer DV-I+(20 RPM, RV6, 30 Seconds, 20° C.) in the range of from 1 Pas to 500 Pas, preferably from 2 Pas to 100 Pas, more preferably from 3 Pas to 50 Pas. 
     “Personal care composition” refers to any product applied to a human body for improving appearance, sun protection, cleansing, odor control, moisturization or general aesthetics. Non-limiting examples of personal care compositions include skin lotions, creams, gels, lotions, facial masks, sticks, shampoos, conditioners, shower gels, toilet bars, antiperspirants, deodorants, shave creams, depilatories, lipsticks, foundations, sunless tanners and sunscreen lotions. 
     “Skin cosmetic composition” refers to any product applied to a human body for improving appearance, sun protection, reducing wrinkled appearance or other signs of photoaging, odor control, skin lightening, even skin tone, or general aesthetics. Non-limiting examples of topical cosmetic skin compositions include skin lotions, creams, facial masks, gels, sticks, antiperspirants, deodorants, lipsticks, foundations, liquid or gel body washes, soap bars, sunless tanners and sunscreen lotions. 
     Personal care composition of the present technology is preferably a leave-on non-solid skin cosmetic composition, because such compositions are the most challenging in terms of incorporating cystine due to its low solubility. 
     Glutathione (“GSH”) Precursor 
     The GSH precursor according to the present invention may comprise the amino acids glycine, glutamate or glutamate source, as well as the cystine and N,N′-diacetyl-L-Cystine (“NDAC”). 
     Amino acids included in the inventive composition are present as L, D, or a mixture of L and D stereo isomers. Preferably, L stereo isomers are employed, and this is the most abundant and natural isomeric form found in nature. 
     Any of the amino acids included in the present invention may be in the form of a salt, ester, or a salt thereof and the term “cystine,” “NDAC,” “glutamate source”, and “glycine” used in the present specification also encompasses salts, esters, and salts of such esters. The salt, ester, and salt of such ester is not particularly limited as long as it is acceptable for topical application. For example, salts with inorganic acid or organic acid or anionic surfactants can be mentioned. As the inorganic acid, for example, hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid and the like can be mentioned, and as the organic acid C 1 -C 18  linear, branched or cyclic, saturated or unsaturated, unsubstituted or substituted with heteroatoms, for example formic acid, acetic acid, trifluoroacetic acid, propionic acid, lactic acid, tartaric acid, oxalic acid, fumaric acid, succinic acid, maleic acid, citric acid, malonic acid, methanesulfonic acid, stearic acid, oleic acid, 12-hydroxystearic acid, ricinoleic acid, and the like can be mentioned. 
     As the salt with a base, for example, alkali metal salts such as sodium salt, potassium salt and the like, alkaline earth metal salts such as calcium salt, magnesium salt, and the like can be mentioned. 
     Esters of amino acids are typically C 1 -C 8  esters or salts thereof, or in the alternative C 1 -C 5  esters, or in the alternative C 1 -C 3  esters. Such esters may be straight or branched or cyclic. Especially, esters of cystine are beneficial, due to their increased solubility, compared to cystine. Methyl and ethyl esters of cystine or salts thereof are most preferred, due to their efficacy to boost glutathione production and provide antioxidant activity. When salts of esters are used, the same salts are suitable as listed above. 
     Glutamate source can be present in the form of its functional equivalents—glutamine, glutamic acid and/or pyroglutamic acid and/or their salts may be employed. Pyroglutamic acid (and/or salts thereof) is preferred since it is more stable than glutamine or glutamic acid. In one embodiment, amino acids in GSH precursor are cystine and pyroglutamic acid (and/or salts thereof). In one embodiment, amino acids in GSH precursor are cystine and pyroglutamic acid and glycine (and/or salts thereof). 
     N,N′-Diacetyl-L-Cystine (“NDAC”) 
     NDAC is an amide, i.e., an N,N′-diacetyl derivative of cystine. NDAC, for purposes of the present invention, has the following chemical structure: 
     
       
         
         
             
             
         
       
     
     Included in the present invention may be NDAC in the form of a salt, ester, or a salt of such ester. 
     Examples of the other SH-containing cystine derivatives which are less advantageous than NDAC are N-Acetyl-L-Cysteine (“NACys”), N-Acetyl-L-Cystine (“NAC”), and L-Cystine diethyl ester (“DEC”, Cystine Ester with Ethyl substituents on CO 2  groups and unsubstituted N groups). 
     NDAC is not readily commercially available but may be sourced on lab scale. NDAC may be synthesized directly from NACys as described in Rathore et al, Organic Letters, 20(19), 6274-6278 (2018) and Pye et al, Green Chemistry, 20(1), 118-124 (2018): 
     
       
         
         
             
             
         
       
     
     A significant advantage of the inventive compositions is that cystine can be solubilized in the presence of NDAC. 
     An amount of NDAC effective to solubilize cystine may be used in accordance with one embodiment. NDAC and cystine are present in the composition in a weight ratio of 1:10000 to 10000:1 of NDAC:cystine; preferably 1000:1 to 5000:1, more preferably 1:1 to 1000:1, in the alternative 4.8:1 (molar 3.5:1), and in another alternative 5.5:1 (molar 4:1). 
     As will be seen from the Examples presented below, NDAC is effective at solubilizing cystine and keeping it in solution by avoiding its crystallization or precipitation in compositions containing them. This effect is achieved at a pH range of 5 to 7. 
     N-Acetyl-L-Cysteine (“NACys”) is structurally similar to NDAC. For example, as mentioned above in the Background section, NDAC may be obtained when NACys is dimerized via a S—S disulfide bridge. NACys is a thiol drug used commonly as an expectorant ( Cryst. Eng. Comm.,  2016, 18, 8587, referred to as “NACe” therein). As will be seen from the Examples presented below, NACys is also effective at inhibiting the crystallization of cystine, however, it provides an upleasant sulfurous odor, that is unacceptable in cosmetic products. Furthermore, the sulfurous odor (monitored as hydrogen sulfide or H 2 S) is consistent with NACys decomposition which is also unacceptable in marketed cosmetic products. 
     Certain cystine esters, such as for example L-Cystine diethyl ester (“DEC”), are more water soluble than cystine. However, as will be seen from the Examples presented below, DEC does not solubilize cystine nor does it prevent cystine crystallization. Furthermore, DEC generates an unpleasant sulfurous odor (monitored as H 2 S) consistent with decomposition, both unacceptable for marketed cosmetic products. 
     Applicant(s) has found that by virtue of including NDAC, the drawback of cystine&#39;s limited solubility is overcome. Furthermore, by virtue of including the NDAC, less cystine may be used for a given level of increase in intracellular production of glutathione 
     In one embodiment, the composition of the invention is a leave-on non-solid composition in the form of a personal care topical emulsion, lotion, gel, cream, or vanishing cream comprising glutathione precursor which comprises NDAC, glutamate (especially pyroglutamic acid or salt thereof, e.g. sodium pyroglutamate), and glycine, at pH of 3.5 to 8.5. 
     In one embodiment, the composition of the invention is a leave-on non-solid composition in the form of a personal care topical emulsion, lotion, gel, cream, or vanishing cream comprising glutathione precursor which comprises cystine, NDAC, glutamate (especially pyroglutamic acid or salt thereof, e.g. sodium pyroglutamate), and glycine, at pH of 3.5 to 8.5, especially at pH of 5 to 8, alternatively at pH of 5 to 7. 
     In one embodiment, the composition of the invention is a leave-on non-solid composition in the form of a personal care topical emulsion, lotion, gel, cream, or vanishing cream comprising glutathione precursor which comprises cystine, NDAC, and glutamate (especially pyroglutamic acid or salt thereof, e.g. sodium pyroglutamate), at pH of 3.5 to 8.5, especially at pH of 5 to 8, alternatively at pH of 5 to 7. 
     In a preferred embodiment, the composition of the invention is a leave-on non-solid composition in the form of a personal care topical emulsion, lotion, gel, cream, or vanishing cream comprising glutathione precursor which comprises cystine and NDAC at a weight ratio of about 4:1 to about 1:4, glutamate (especially pyroglutamic acid or salt thereof, e.g. sodium pyroglutamate), at pH of 3.5 to 8.5, especially at pH of 5 to 8, alternatively at pH of 5 to 7. For aqueous solubility, the optimum ratio of NDAC: Cystine is 4:1 on a Molar basis. This is equivalent to 55 mg NDAC:10 mg Cystine on a weight basis, as the molecular weights of NDAC=324.4 and Cystine=240.3. 
     Amounts of Glutathione Precursors 
     NDAC is included in an amount of from 0.01 to 5%, or in the alternative of from to 0.5 to 5%, or from 1% to 5%, or in the alternative from 2% to 5% by weight of the composition. 
     Cystine is included in an amount of from 0.001 to 2%, or in the alternative of from to 0.005 to 1%, or from 0.008 to 0.5%, or in the alternative from 0.008 to 0.4%. 
     In one embodiment, glutamate source (preferably pyroglutamate) is included in an amount of from 0.01 to 10%, or in the alternative of from to 0.01 to 5%, or from 0.05 to 1%, or in the alternative from 0.05 to 0.5%. 
     In one embodiment, glycine source is included in an amount of from 0.01 to 10%, or in the alternative of from to 0.01 to 5%, or from 0.01 to 1%, or in the alternative from 0.01 to 0.2%, or in the alternative from 0.01 to 0.1%. 
     The total weight of NDAC is at least twice as much as the weight of the amino acids. In one embodiment, the weight ratio of NDAC to total amino acids is in the range of from 15:1 to 3:1. In the alternative, the weight ratio of NDAC to total amino acids is in the range of from 15:1 to 2:1. Preferably, the weight ratio of NDAC to cystine is greater than 5.5:1 to 1:1; in the alternative 5:1; preferably in another alternative 4:1; preferably 5.5:1. 
     Carrier 
     Compositions of this invention also include a cosmetically acceptable carrier. Amounts of the carrier may range from 1 to 99.9%, preferably from 70 to 95%, optimally from 80 to 90%. Among the useful carriers are water, emollients, fatty acids, fatty alcohols, thickeners and combinations thereof. The carrier may be aqueous, anhydrous or an emulsion. Preferably the compositions are aqueous, especially water and oil emulsions of the water-in-oil or oil-in-water type or multiple emulsions of the water-in-oil-in-water or oil-in-water-in-oil variety. Water when present may be in amounts ranging from 5 to 95%, preferably from about 20 to about 70%, optimally from 35 to 60% by weight. 
     Emollient materials may serve as cosmetically acceptable carriers. These may be in the form of silicone oils, natural or synthetic esters, hydrocarbons, alcohols and fatty acids. Amounts of the emollients may range anywhere from 0.1 to 95%, preferably between 1 and 50% by weight of the composition. 
     Silicone oils may be divided into the volatile and nonvolatile variety. The term “volatile” as used herein refers to those materials which have a measurable vapor pressure at ambient temperature. Volatile silicone oils are preferably chosen from cyclic (cyclomethicone) or linear polydimethylsiloxanes containing from 3 to 9, preferably from 5 to 6, silicon atoms. Nonvolatile silicone oils useful as an emollient material include polyalkyl siloxanes, polyalkylaryl siloxanes and polyether siloxane copolymers. The essentially nonvolatile polyalkyl siloxanes useful herein include, for example, polydimethyl siloxanes with viscosities of from 5×10 −6  to 0.1 m 2 /s at 25° C. Among the preferred nonvolatile emollients useful in the present compositions are the polydimethyl siloxanes having viscosities from 1×10 −5  to about 4×10 −4  m 2 /s at 25° C. 
     Another class of nonvolatile silicones are emulsifying and non-emulsifying silicone elastomers. Representative of this category is Dimethicone/Vinyl Dimethicone Crosspolymer available as Dow Corning 9040, General Electric SFE 839, and Shin-Etsu KSG-18. Silicone waxes such as Silwax WS-L (Dimethicone Copolyol Laurate) may also be useful. 
     Among the ester emollients are: 
     a) Alkyl esters of saturated fatty acids having 10 to 24 carbon atoms. Examples thereof include behenyl neopentanoate, isononyl isonanonoate, isopropyl myristate and octyl stearate. 
     b) Ether-esters such as fatty acid esters of ethoxylated saturated fatty alcohols. 
     c) Polyhydric alcohol esters. Ethylene glycol mono and di-fatty acid esters, diethylene glycol mono- and di-fatty acid esters, polyethylene glycol (200-6000) mono- and di-fatty acid esters, propylene glycol mono- and di-fatty acid esters, polypropylene glycol 2000 monostearate, ethoxylated propylene glycol monostearate, glyceryl mono- and di-fatty acid esters, polyglycerol poly-fatty esters, ethoxylated glyceryl mono-stearate, 1,3-butylene glycol monostearate, 1,3-butylene glycol distearate, polyoxyethylene polyol fatty acid ester, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters are satisfactory polyhydric alcohol esters. Particularly useful are pentaerythritol, trimethylolpropane and neopentyl glycol esters of C 1 -C 30  alcohols. 
     d) Wax esters such as beeswax, spermaceti wax and tribehenin wax. 
     e) Sugar ester of fatty acids such as sucrose polybehenate and sucrose polycottonseedate. 
     Natural ester emollients principally are based upon mono-, di- and tri-glycerides. Representative glycerides include sunflower seed oil, cottonseed oil, borage oil, borage seed oil, primrose oil, castor and hydrogenated castor oils, rice bran oil, soybean oil, olive oil, safflower oil, shea butter, jojoba oil and combinations thereof. Animal derived emollients are represented by lanolin oil and lanolin derivatives. Amounts of the natural esters may range from 0.1 to 20% by weight of the compositions. 
     Hydrocarbons which are suitable cosmetically acceptable carriers include petrolatum, mineral oil, C 11 -C 13  isoparaffins, polybutenes and especially isohexadecane, available commercially as Permethyl 101A from Presperse Inc. 
     Fatty acids having from 10 to 30 carbon atoms may also be suitable as cosmetically acceptable carriers. Illustrative of this category are pelargonic, lauric, myristic, palmitic, stearic, isostearic, oleic, linoleic, linolenic, hydroxystearic and behenic acids and mixtures thereof. 
     Fatty alcohols having from 10 to 30 carbon atoms are another useful category of cosmetically acceptable carrier. Illustrative of this category are stearyl alcohol, lauryl alcohol, myristyl alcohol, oleyl alcohol and cetyl alcohol and mixtures thereof. 
     Thickeners or rheology modifiers can be utilized as part of the cosmetically acceptable carrier of compositions according to the present invention. Typical thickeners include crosslinked acrylates (e.g. Carbopol 982®), hydrophobically-modified acrylates (e.g. Carbopol 1382®), polyacrylamides (e.g. Sepigel 305®), acryloylmethylpropane sulfonic acid/salt polymers and copolymers (e.g. Aristoflex HMB® and AVC®), cellulosic derivatives and natural gums. Among useful cellulosic derivatives are sodium carboxymethylcellulose, hydroxypropyl methylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, ethyl cellulose and hydroxymethyl cellulose. Natural gums suitable for the present invention include guar, xanthan, sclerotium, carrageenan, pectin and combinations of these gums. Inorganics may also be utilized as thickeners, particularly clays such as bentonites and hectorites, fumed silicas, talc, calcium carbonate and silicates such as magnesium aluminum silicate (Veegum®). Amounts of the thickener may range from 0.0001 to 10%, usually from 0.001 to 1%, or from 0.01 to 0.5%. 
     Preferred are emollients that can be used, especially for products intended to be applied to the face, to improve sensory properties and are chosen from the group of polypropylene glycol-14 butyl ether otherwise known as Tegosoft PBE, or PPG15 stearyl ether such as Tegosoft E, other oils such as esters, specifically, isopropyl myristate, isopropyl palmitate, other oils could include castor oils and derivatives thereof. 
     Humectants of the polyhydric alcohol-type can be employed as cosmetically acceptable carriers. Typical polyhydric alcohols include glycerol, polyalkylene glycols and more preferably alkylene polyols and their derivatives, including propylene glycol, dipropylene glycol, polypropylene glycol, polyethylene glycol and derivatives thereof, sorbitol, hydroxypropyl sorbitol, hexylene glycol, 1,3-butylene glycol, isoprene glycol, 1,2,6-hexanetriol, ethoxylated glycerol, propoxylated glycerol and mixtures thereof. The amount of humectant may range anywhere from 0.5 to 50%, preferably between 1 and 15% by weight of the composition. 
     Skin moisturizers, e.g. hyaluronic acid and/or its precursor N-acetyl glucosamine may be included. N-acetyl glucosamine may be found in shark cartilage or shitake mushrooms and are available commercially from Maypro Industries, Inc (New York). Other preferred moisturizing agents include hydroxypropyl tri(C 1 -C 3  alkyl)ammonium salts. These salts may be obtained in a variety of synthetic procedures, most particularly by hydrolysis of chlorohydroxypropyl tri(C 1 -C 3  alkyl)ammonium salts. A most preferred species is 1,2-dihydroxypropyltrimonium chloride, wherein the C 1 -C 3  alkyl is a methyl group. Amounts of the salt may range from 0.2 to 30%, and preferably from 0.5 to 20%, optimally from 1% to 12% by weight of the topical composition, including all ranges subsumed therein. 
     Ordinarily the C 1 -C 3  alkyl constituent on the quaternized ammonium group will be methyl, ethyl, n-propyl, isopropyl or hydroxyethyl and mixtures thereof. Particularly preferred is a trimethyl ammonium group known through INCI nomenclature as a “trimonium” group. Any anion can be used in the quat (quaternized) salt. The anion may be organic or inorganic with proviso that the material is cosmetically acceptable. Typical inorganic anions are halides, sulfates, phosphates, nitrates and borates. Most preferred are the halides, especially chloride. Organic anionic counter ions include methosulfate, toluoyl sulfate, acetate, citrate, tartrate, lactate, gluconate, and benzenesulfonate. 
     Still other preferred moisturizing agents which may be used, especially in conjunction with the aforementioned ammonium salts include substituted urea like hydroxymethyl urea, hydroxyethyl urea, hydroxypropyl urea; bis(hydroxymethyl) urea; bis(hydroxyethyl) urea; bis(hydroxypropyl) urea; N,N′-dihydroxymethyl urea; N,N′-di-hydroxyethyl urea; N,N′-di-hydroxypropyl urea; N,N,N′-tri-hydroxyethyl urea; tetra(hydroxymethyl) urea; tetra(hydroxyethyl) urea; tetra(hydroxypropyl urea; N-methyl, N′-hydroxyethyl urea; N-ethyl-N′-hydroxyethyl urea; N-hydroxypropyl-N′-hydroxyethyl urea and N,N′dimethyl-N-hydroxyethyl urea. Where the term hydroxypropyl appears, the meaning is generic for either 3-hydroxy-n-propyl, 2-hydroxy-n-propyl, 3-hydroxy-i-propyl or 2-hydroxy-i-propyl radicals. Most preferred is hydroxyethyl urea. The latter is available as a 50% aqueous liquid from the National Starch &amp; Chemical Division of ICI under the trademark “Hydrovance.” Amounts of substituted urea that may be used in the topical composition of this invention range from 0.01 to 20%, or from 0.5 to 15%, or from 2 to 10%. 
     When ammonium salt and substituted urea are used, in a most especially preferred embodiment at least from 0.01 to 25%, or from 0.2 to 20%, or from 1 to 15% humectant, like glycerin, is used. Further moisturizing agents for use herein include petrolatum and/or various aquaporin manipulating actives and/or oat kernel flour. 
     pH of the Composition 
     Cystine is only soluble in aqueous solution or personal care compositions at very low or very high pH. 
     In one embodiment, the pH of the personal care composition is between 3.5 and 8.5. In some embodiments, the pH of the personal care composition is between pH 3.5 and pH 8. In some embodiments, the pH of the personal care composition is between pH 5 to pH 7.8. In some embodiments, the pH of the personal care composition is between 5 and 7.5. 
     Preferred Optional Ingredients 
     In some embodiments, the personal care composition, and especially a leave-on skin cosmetic composition of the present invention contains sun-screen. These are typically a combination of organic and inorganic sunscreens. It is particularly important to include both UV-A and UV-B radiation sunscreens. 
     UV-B sunscreen oil may be selected from the class of cinnamic acid, salicylic acid, diphenyl acrylic acid, or derivatives thereof. The UV-B sunscreen oil may include one or more of octyl salicylate, 3,3,5-trimethylcyclohexyl 2-hydroxybenzoate, ethylhexyl salicylate, 2-ethylhexyl 2-cyano-3,3-diphenyl-2-propenoate, or 2-ethylhexyl-4-methoxycinnamate (also known as octyl methoxycinnamate or “OMC”). Such UV-B sunscreen oils are typically commercially available, such as Octisalate™ (octyl salicylate), Homosalate™ (3,3,5-trimethyleyclohexyl 2-hydroxybenzoate), NeoHeliopan™ (a range of organic UV filters including OMC (Neo Heliopan AV™) and ethylhexyl salicylate (Neo Heliopan OS™)), Octocrylene™ and Milestab 3039™ (2 ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate) or Parsol MCX™ (2-ethylhexyl-4-methoxycinnamate). The amount of UV-B sunscreen oil in the personal care composition may be 0.1 wt % to 20 wt %, or 0.2 wt % to 10 wt %, or 0.5 wt % to 7 wt %, or 2 wt % to 6 wt %. 
     The personal care composition may further include a UV-B sunscreen that is water-soluble. The water soluble UV-B sunscreen may also include phenylbezimidazole sulfonic acid (also known as ensulizole), 4-aminobenzoic acid (also known as para-aminobenzoic acid or “PABA”), or both. 
     The personal care composition of any one of the above embodiments may further include 0.1 wt % to 10 wt % of a UV-A sunscreen oil. The UV-A sunscreen oil may include one or more of 4-t-butyl-4′-methoxydibenzoylmethane (“avobenzone”), 2-methyldibenzoylmethane, 4-methyl-dibenzoyl-ethane, 4-isopropyldibenzoyl-methane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane, 2,5-dimethyldibenzoylmethane, 4,4′-diisopropyldibenzoylmethane, 2-methyl-5-isopropyl-4′-methoxy-dibenzoylmethane, 2-methyl-5-tert-butyl-4′-methoxy-dibenzoylmethane, 2,4-dimethyl-4′-methoxydibenzoylmethane, 2,6-dimehyl-4-tert-butyl-4′methoxy-dibenzoylmethane, diethylaminohydroxybenzoyl hexyl benzoate, ecamsule, or methyl anthranilate. The amount of UV-A sunscreen oil in the personal care composition may be 0.5 wt % to 7 wt %, or 1 wt % to 5 wt %. 
     Additional suitable sunscreen oils suitable for use in the personal care composition include those commercially available from BASF corporation: Uvinul T-150 (Ethylhexyl triazone; a UV-B sunscreen oil), Uvinul A Plus (Diethylamino hydroxybenzoyl hexyl benzoate; a UV-A sunscreen oil), Tinosorb S (bis-ethylhexyloxyphenol methoxyphenyl triazine; a UV-A and UV-B sunscreen oil), Tinosorb M(methylene bisbenzotriazolyl tetramethylbutylphenol; a UV-A and UV-B sunscreen oil). Bisdisulizone disodium may also be included in the personal care composition. 
     A particularly preferred combination of UV-A and UV-B sunscreen oils is avobenzone and 2-ethylhexyl-4-methoxycinnamate. 
     In some embodiments, the sunscreen is an inorganic sunscreen. Examples of inorganic sunscreens suitable for use in the skin care composition of the present invention include, but are not limited to, microfine titanium dioxide, zinc oxide, polyethylene and various other polymers. By the term “microfine” is meant particles of average size ranging from 10 to 200 nm, alternatively from 20 to 100 nm. Amounts of the sunscreen when present in a skin care formulation according to some embodiments of the present invention may range from 0.1% to 30%, alternatively from 2% to 20%, alternatively from 4% to 10%. 
     It has been taught that a selenium source, e.g. selenomethionine, is an essential ingredient, along with constituent amino acids of GSH, for enabling GSH intracellular biosynthesis; the transsulfuration pathway (also called the cystathionine pathway) allows the utilization of methionine for GSH synthesis. Surprisingly, it has been found as part of the present invention, however, that a selenium source is not necessary, and is indeed superfluous, to achieve intracellular increase in GSH content according to the present invention. Although selenium source may be included, it is preferably avoided in topical skin care compositions of the invention because it is considered a skin sensitizer under some regulatory regimes. Accordingly, the amount of selenium in the present compositions is from 0 to maximum 0.1%, or at most 0.05%, optimally no more than 0.01%. 
     The inventive composition preferably includes a skin lightening compound, to obtain optimum skin lightening performance at an optimum cost. Illustrative substances are placental extract, lactic acid, niacinamide, arbutin, kojic acid, ferulic acid, hydroquinone, resorcinol derivatives including mono-substituted (4-substituted) and di-substituted (2,5-disubstituted, 4,5-disubstituted, and 4,6 di-substituted) resorcinols and combinations thereof. More preferably, such skin lightening compound is a tyrosinase inhibitor, most preferably a compound selected from the group consisting of kojic acid, hydroquinone and other (non-4 substituted resorcinols). Also, dicarboxylic acids represented by the formula HOOC−(CxHy)—COOH where x=4 to 20 and y=6 to 40 such as azelaic acid, sebacic acid, oxalic acid, succinic acid, fumaric acid, octadecenedioic acid (e.g. Arlatone DC) or their salts or a mixture thereof, most preferably fumaric acid or salt thereof, especially di-sodium salt. It has been found that combination with 12-hydroxystearic acid (12HSA) and with fumaric acid or salts thereof are particularly preferred, especially for skin lightening formulations. Amounts of these agents may range from 0.1 to 10%, preferably from 0.5 to 2%. It is preferred that the skin lightening coactive according to the invention is vitamin B3 or a derivative thereof and is selected from the group consisting of niacinamide, nicotinic acid esters, non-vasodilating esters of nicotinic acid, nicotinyl amino acids, nicotinyl alcohol esters of carboxylic acids, nicotinic acid N-oxide, niacinamide N-oxide and mixtures thereof. 
     Another preferred ingredient of the inventive compositions is a retinoid. As used herein, “retinoid” includes all natural and/or synthetic analogs of Vitamin A or retinol-like compounds which possess the biological activity of Vitamin A in the skin as well as the geometric isomers and stereoisomers of these compounds. The retinoid is preferably retinol, retinol esters (e.g., C 2 -C 22  alkyl esters of retinol, including retinyl palmitate, retinyl acetate, retinyl propionate), retinal, and/or retinoic acid (including all-trans retinoic acid and/or 13-cis-retinoic acid), more preferably retinoids other than retinoic acid. These compounds are well known in the art and are commercially available from a number of sources, e.g., Sigma Chemical Company (St. Louis, Mo.), and Boerhinger Mannheim (Indianapolis, Ind.). Other retinoids which are useful herein are described in U.S. Pat. Nos. 4,677,120, issued Jun. 30, 1987 to Parish et al.; U.S. Pat. No. 4,885,311, issued Dec. 5, 1989 to Parish et al.; U.S. Pat. No. 5,049,584, issued Sep. 17, 1991 to Purcell et al.; U.S. Pat. No. 5,124,356, issued Jun. 23, 1992 to Purcell et al.; and U.S. Pat. No. Reissue 34,075, issued Sep. 22, 1992 to Purcell et al. Other suitable retinoids are tocopheryl-retinoate [tocopherol ester of retinoic acid (trans- or cis-), adapalene {6-[3-(1-adamantyl)-4-methoxyphenyl]-2-naphthoic acid}, and tazarotene (ethyl 6-[2-(4,4-dimethylthiochroman-6-yl)-ethynyl]nicotinate). Preferred retinoids are retinol, retinyl palmitate, retinyl acetate, retinyl propionate, retinal and combinations thereof. The retinoid is preferably substantially pure, more preferably essentially pure. The compositions of this invention may contain a safe and effective amount of the retinoid, such that the resultant composition is safe and effective for regulating keratinous tissue condition, preferably for regulating visible and/or tactile discontinuities in skin, more preferably for regulating signs of skin aging, even more preferably for regulating visible and/or tactile discontinuities in skin texture associated with skin aging. The compositions preferably contain from 0.005% to 2%, or from 0.01% to 2%, retinoid. Retinol is preferably used in an amount of 0.01% to 0.15%; retinol esters are preferably used in an amount of from 0.01% to 2% (e.g., 1%); retinoic acids are preferably used in an amount of 0.01% to 0.25%; tocopheryl-retinoate, adapalene, and tazarotene are preferably used in an amount of from 0.01% to 2%. 
     A variety of herbal extracts may optionally be included in compositions of this invention. Illustrative are pomegranate, white birch ( Betula Alba ), wasabi, green tea, chamomile, licorice, and extract combinations thereof. The extracts may either be water soluble or water-insoluble carried in a solvent which respectively is hydrophilic or hydrophobic. Water and ethanol are the preferred extract solvents. 
     Also included may be such materials as resveratrol, alpha-lipoic acid, ellagic acid, kinetin, retinoxytrimethylsilane (available from Clariant Corp. under the Silcare 1M-75 trademark), dehydroepiandrosterone (DHEA) and combinations thereof. Ceramides (including Ceramide 1, Ceramide 3, Ceramide 3B, Ceramide 6 and Ceramide 7) as well as pseudoceramides may also be utilized for many compositions of the present invention but may also be excluded. Amounts of these materials may range from 0.000001 to 10%, preferably from 0.0001 to 1%. 
     The personal care composition may further include about 0.1 wt % to about 8 wt % of a film forming polymer. Such film-forming polymers include, but are not limited to, polyalkyleneoxy terminated polyamides (e.g., INCI name: Polyamide-3, Polyamide-4), polyether polyamides (e.g., INCI name: Polyamide-6), mixed acid terminated polyamides (e.g., INCI name: Polyamide-7), and ester terminated poly(ester-amides) (e.g., INCI name: Polyamide-8). Such film forming polymers may be synthesized or are available commercially, such as under the Sylvaclear™ line of products by Arizona Chemical Company, LLC and the OleoCraft™ line of products by Croda International PLC. Film-forming polymers also include, but are not limited to, the INCI named Polyester-5 (e.g., Eastman AQ™ 38S Polymer), PPG-17/IPDI/DMPA Copolymer (e.g., Avalure™ UR 450 Polymer), Acrylates Copolymer (e.g., Avalure™ AC 120 Polymer), and polysaccharides such as Xilogel (tamarin gum), lotus bean gums, tara gum, beta glucan, pullulan, carboxymethyl cellulose, hydroxypropyl cellulose, sodium alginate, potato starch, carrageenan. The film forming polymer may include combinations of any two or more of the polymers recited above. The amount of film forming polymer in the personal care composition may be 0.1 wt % to 8 wt %. 
     Preservatives can desirably be incorporated into the compositions of this invention to protect against the growth of potentially harmful microorganisms. Suitable traditional preservatives for compositions of this invention are alkyl esters of para-hydroxybenzoic acid. Other preservatives which have more recently come into use include hydantoin derivatives, propionate salts, and a variety of quaternary ammonium compounds. Cosmetic chemists are familiar with appropriate preservatives and routinely choose them to satisfy the preservative challenge test and to provide product stability. Particularly preferred preservatives are iodopropynyl butyl carbamate, phenoxyethanol, caprylyl glycol, C 1-6  parabens (especially, methyl paraben and/or propyl paraben), imidazolidinyl urea, sodium dehydroacetate and benzyl alcohol. The preservatives should be selected having regard for the use of the composition and possible incompatibilities between the preservatives and other ingredients in the emulsion. Preservatives are preferably employed in amounts ranging from 0.01% to 2%. An especially preferred combination is octocrylene and caprylyl glycol, since caprylyl glycol has been disclosed to enhance UVA and UVB protection. 
     Anti-fungal agents suitable for inclusion in personal care compositions are well known to one of skill in the art. Examples include, but are not limited to, climbazole, ketoconazole, fluconazole, clotrimazole, miconazole, econazole, etaconazole, terbinafine, salts of any one or more of these (e.g., hydrochloride salts), zinc pyrithione, selenium disulfide, and combinations of any two or more thereof. 
     In some embodiments, the personal care compositions of the present invention include vitamins. Illustrative vitamins are Vitamin A (retinol), Vitamin B2, Vitamin B3 (niacin), Vitamin B6, Vitamin B12, Vitamin C, Vitamin D, Vitamin E, Vitamin K and Biotin. Derivatives of the vitamins may also be employed. For instance, Vitamin C derivatives include ascorbyl tetraisopalmitate, magnesium ascorbyl phosphate and ascorbyl glycoside. Derivatives of Vitamin E include tocopheryl acetate, tocopheryl palmitate and tocopheryl linoleate. DL-panthenol and derivatives may also be employed. In some embodiments, the Vitamin B6 derivative is Pyridoxine Palmitate. In some embodiments, the Vitamin B3 derivative is nicotinamide riboside. Flavonoids may also be useful, particularly glucosyl hesperidin, rutin, and soy isoflavones (including genistein, daidzein, equol, and their glucosyl derivatives) and mixtures thereof. Total amount of vitamins or flavonoids when present may range from 0.0001% to 10%, alternatively from 0.001% to 10%, alternatively from 0.01% to 10%, alternatively from 0.1% to 10%, alternatively from 1% to 10%, alternatively from 0.01% to 1%, alternatively from 0.1% to 0.5%. 
     In some embodiments, the personal care compositions of the present invention include an enzyme such as, for example oxidases, proteases, lipases and combinations thereof. In some embodiments, the personal care compositions of the present invention includes superoxide dismutase, commercially available as Biocell SOD from the Brooks Company, USA. 
     In some embodiments, the personal care compositions of the present invention include desquamation promoters. In some embodiments, the personal care compositions of the present invention include desquamation promoters at a concentration from 0.01% to 15%, alternatively from 0.05% to 15% alternatively from 0.1% to 15%, alternatively from 0.5% to 15% 
     Illustrative desquamation promoters include monocarboxylic acids. Monocarboxylic acids may be substituted or unsubstituted with a carbon chain length of up to 16. In some embodiments, the carboxylic acids are the alpha-hydroxycarboxylic acids, beta-hydroxycarboxylic or polyhydroxycarboxylic acids. The term “acid” is meant to include not only the free acid but also salts and C 1 -C 30  alkyl or aryl esters thereof and lactones generated from removal of water to form cyclic or linear lactone structures. Representative acids include glycolic, lactic, malic, and tartaric acids. In some embodiments, the salt is ammonium lactate. In some embodiments, the beta-hydroxycarboxylic acid is salicylic acid. In some embodiments, the phenolic acids include ferulic acid, salicylic acid, kojic acid, and their salts. 
     In some embodiments, the at least one additional component may be present from 0.000001% to 10%, alternatively from 0.00001% to 10%, alternatively from 0.0001% to 10%, alternatively from 0.001% to 10%, alternatively from 0.01% to 10%, alternatively from 0.1% to 10%, alternatively from 0.0001% to 1% by weight of the composition. Colorants, opacifiers or abrasives may also be included in compositions of the present invention. The colorants, opacifiers or abrasives may be included at a concentration from 0.05% to 5%, alternatively between 0.1% and 3% by weight of the composition. 
     In some embodiments, the personal care product of the present invention may also include a peptide, such as, for example, the commercially available pentapeptide derivative-Matrixyl™, which is commercially available from Sederma, France. In another example, in some embodiments, the personal care product of the present invention may also include Carnosine. 
     The compositions of the present invention can comprise a wide range of other optional components. The CTFA Cosmetic Ingredient Handbook, Second Edition, 1992, which is incorporated by reference herein in its entirety, describes a wide variety of non-limiting cosmetic and pharmaceutical ingredients commonly used in the topical cosmetic skin care industry, which are suitable for use in the compositions of the present invention. Examples include: antioxidants, binders, biological additives, buffering agents, colorants, thickeners, polymers, astringents, fragrance, humectants, opacifying agents, conditioners, exfoliating agents, pH adjusters, preservatives, natural extracts, essential oils, skin sensates, skin soothing agents, and skin healing agents. 
     Form of the Composition 
     The compositions of the present invention are preferably non-solid. The compositions of the invention are preferably leave-on compositions. The compositions of the present invention are preferably leave-on compositions to be applied to remain on the skin. These leave-on compositions are to be distinguished from compositions which are applied to the skin and subsequently removed either by washing, rinsing, wiping, or the like either after or during the application of the product. Surfactants typically used for rinse-off compositions have physico-chemical properties giving them the ability to generate foam/lather in-use with ease of rinse; they can consist of mixtures of anionic, cationic, amphoteric, and nonionic. Surfactants used in leave-on compositions on the other hand are not required to have such properties. Rather, as leave-on compositions are not intended to be rinsed-off they need to be non-irritating and therefore it is necessary to minimize the total level of surfactant and the total level of anionic surfactant in leave-on compositions. The total level of surfactant in the inventive compositions is preferably from 1% no more than 15%, more preferably below 10%, most preferably at most 9%, optimally at most 6%. 
     In some embodiments, anionic surfactants are present in the leave-on skin care composition in an amount of 0.01% to at most 5% by weight of the composition, alternatively from 0.01% to 4% by weight of the composition, alternatively from 0.01% to 3% by weight of the composition, alternatively from 0.01% to 2% by weight of the composition, alternatively substantially absent (less than 1%, or less than 0.1%, or less than 0.01%). In some embodiments, the total level of surfactant in the skin care compositions is no more than 15%, alternatively below 10%, alternatively at most 9%. 
     In some embodiments, the surfactant is selected from the group consisting of anionic, nonionic, cationic and amphoteric actives. 
     In some embodiments, nonionic surfactants are those with a C 10 -C 20  fatty alcohol or acid hydrophobe condensed with from 2 to 100 moles of ethylene oxide or propylene oxide per mole of hydrophobe; C 2 -C 10  alkyl phenols condensed with from 2 to 20 moles of alkylene oxide; mono- and di-fatty acid esters of ethylene glycol; fatty acid monoglyceride; sorbitan, mono- and di-C 8 -C 20  fatty acids; and polyoxyethylene sorbitan as well as combinations thereof. In some embodiments, the non-ionic surfactant is selected from the group consisting of alkyl polyglycosides, saccharide fatty amides (e.g. methyl gluconamides) and trialkylamine oxides. 
     Amphoteric surfactants suitable in skin care compositions according to some embodiments of the present invention include cocoamidopropyl betaine, C 12 -C 20  trialkyl betaines, sodium lauroamphoacetate, and sodium laurodiamphoacetate. 
     Anionic surfactants suitable in skin care compositions according to some embodiments of the present invention include soap, alkyl ether sulfates and sulfonates, alkyl sulfates and sulfonates, alkylbenzene sulfonates, alkyl and dialkyl sulfosuccinates, C 8 -C 20  acyl isethionates, C 8 -C 20  alkyl ether phosphates, C 8 -C 20  sarcosinates, C 8 -C 20  acyl lactylates, sulfoacetates and combinations thereof. 
     The compositions of the present invention are typically in the form of emulsions, which may be oil-in-water, or water-in-oil. 
     In some embodiments the personal care compositions are vanishing creams and creams or lotions based on an oil-in-water emulsion. Vanishing cream base is one which comprises 5 to 40% fatty acid and 0.1 to 20% soap. In such creams, the fatty acid is preferably substantially a mixture of stearic acid and palmitic acid and the soap is preferably the potassium salt of the fatty acid mixture, although other counterions and mixtures thereof can be used. The fatty acid in vanishing cream base is often prepared using hysteric acid which is substantially (generally about 90 to 95%) a mixture of stearic acid and palmitic acid. A typical hysteric acid comprises about 52-55% palmitic acid and 45-48% stearic acid of the total palmitic-stearic mixture. Thus, inclusion of hysteric acid and its soap to prepare the vanishing cream base is within the scope of the present invention. It is particularly preferred that the composition comprises higher than 7%, preferably higher than 10%, more preferably higher than 12% fatty acid. A typical vanishing cream base is structured by a crystalline network and is sensitive to the addition of various ingredients. 
     In one embodiment, the personal care composition is formulated as a water-in-oil emulsion with NDAC and cystine substantially solubilized in the aqueous phase. In one embodiment, the personal care composition is formulated as a water-in-oil emulsion with NDAC and cystine in the aqueous droplets, with at least 90% of the droplets having a diameter in the range of from 100 nm to 20 microns, or in the alternative from 200 nm to 20 microns, or to 10 microns. 
     In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a facial mask. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a facial mask according to the formulations described in U.S. Pat. No. 5,139,771. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a facial mask according to the formulations described in U.S. Pat. No. 4,933,177. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a facial mask according to the formulations described in U.S. Pat. No. 6,001,367. 
     In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a shampoo. In some embodiments, the personal care compositions of the present invention are formulated as a deodorant. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a deodorant according to the formulations described in U.S. Pat. No. 7,282,471. In some embodiments, the personal care compositions of the present invention are formulated as an antiperspirant. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as an antiperspirant according to the formulations described in U.S. Pat. No. 7,282,471. 
     In some embodiments, the personal care compositions of the present invention are formulated as a single use personal care towelette product. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a single use personal care towelette product according to the formulations described in U.S. Pat. No. 7,282,471. 
     In some embodiments, the personal care compositions of the present invention are formulated as a soap bar. In some embodiments, in addition to containing the GSH precursor, the personal care composition is formulated as a soap bar according to the formulations described in U.S. Pat. No. 7,282,471. 
     Methods of Making Skin Care Compositions 
     In some embodiments, skin care compositions according to the present invention can be made by:
         a. mixing all water soluble ingredients including preservatives, thickening polymer, optionally glycerine, and water;   b. heating the mixture to a temperature of 70-90° C.;   c. mixing all the oil soluble ingredients and the compound of formula (1) to a temperature of 70-90° C.;   d. adding the mixed oil soluble ingredients to the heated mixture of water soluble ingredients, and mixing via agitation, maintaining the mixture at a temperature of 70-90° C.; and   e. cooling the mixture to room temperature, whilst mixing.       

     In some embodiments the personal care compositions of the invention are prepared by making an emulsion:
         a. solubilizing NDAC and cystine at the desired level in high pH (9 to 14, or 9 to 12) aqueous solution;   b. preparing a macroemulsion in oil with this solution with an emulsifier, then   c. adding, with mixing, an acidic aqueous solution to obtain an emulsion with pH within a neutral range required for the topical composition and, lastly,   d. subjecting the emulsion to high shear, or homogenization, or sonolation step e.g. via a homogenizer such as Nano DeBee homogenizer of BEE International (Massachusetts, USA) or a Sonolator homogenizer manufactured by Sonic Corporation (Connecticut, USA), to produce a homogeneous neutral pH range final emulsion with more than 90% of the droplets having a diameter in the size range of from 100 nm to 20 microns.       

     Method of Using the Skin Care Compositions 
     In some embodiments, the skin care composition is topically applied to human skin. In some embodiments, the skin care composition provides at least one benefit, selected from the group consisting of: skin conditioning, skin smoothening, reduction of wrinkled or aged skin, reduction of inflammation of the skin, reduction of dryness, reduction of age spots, reduction of sun burn, and lightening of the skin. 
     In some embodiments, a small quantity of the skin care composition, for example from 1 to 5 ml, is applied to exposed area of the skin, from a suitable container or applicator and, if necessary, it is then spread over and/or rubbed into the skin using the hand or fingers or a suitable device. 
     Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in non-limiting examples. 
     EXAMPLES 
     Experimental Methods 
     All amino acids were L stereo isomers. 
     L-Cystine and N-Acetyl-L-cysteine (NACys) were purchased from Sigma. N,N′-Diacetyl-L-cystine (NDAC) was purchased from CombiBlocks. L-Cystine diethyl ester dihydrochloride (DEC) was purchased from Bachem. 
     Sodium pyroglutamic acid (also known as sodium pyrrolidone carboxylate (NaPCA)) was supplied as a 50% solution in water from Ajinomoto. Cystine stock solutions for GSH precursor mixtures (e.g. glycine+glutamate or glutamate source+cystine) were generated in 0.5M sodium hydroxide (pH 12) as cystine is poorly soluble in neutral solutions. To generate the GSH precursor mixture henceforth described as GAP, appropriate volumes of three amino acids (glutamate source (i.e NaPCA), cystine, and glycine) were combined in Hank&#39;s Balanced Salt Solution (Sigma) such that the glutamate source, cystine, and glycine were in a 0.5:1:1 weight ratio. The specific concentrations used in each assay are referenced below.
         Abbreviations in the Examples are as follows:   mM=millimolar   uM=micromolar   uL=micro liter   Glutathione precursor blend=glutamate and cystine and glycine mix       

     Example I 
     Evaluation of Cystine Crystallization and Odor in the Presence of Cystine Derivatives Samples for cystine crystallization evaluation were prepared by dissolving cystine (10 mg) alone or in combination with NDAC (N,N′-diacetyl-L-cystine) (55 mg), NACys (N-acetyl-L-cysteine) (28 mg) or L-cystine diethyl ester dihydrochloride (DEC) (62 mg) in 0.775M NaOH (1 ml) or Epilife™ cell culture media (60 uM calcium chloride, HEPES/bicarbonate buffered; Thermofisher Scientific) (1 ml) and the pH adjusted to 7.0 by adding HCl (12.1M). A hydrogen sulfide (H 2 S) test strip (Sigma) was placed above the sample solution and the samples sealed. Visual appearance, odor and H 2 S generation (unchanged test strip white color=no H 2 S generated; changed test strip brown/black color=H 2 S generated) were monitored up to 4 months and recorded. 
     The results are shown in the Table below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Effect of Cystine Derivatives (NDAC, NACys and DEC) on Cystine 
               
               
                 Crystallization after 4 months at R.T. (~20-22° C.): 
               
            
           
           
               
               
               
               
               
            
               
                 Example 
                   
                   
                   
                 H 2 S Detected 
               
               
                 No. 
                 Sample 
                 Appearance 
                 Odor 
                 ? 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1-A 
                 1% cystine 
                 precipitate 
                 none 
                 no 
               
               
                 2 
                 1% cystine + 
                 clear a 
                 none 
                 no 
               
               
                   
                 3.5% NDAC 
                   
                   
                   
               
               
                 3 
                 1% cystine + 
                 clear 
                 none 
                 no 
               
               
                   
                 4% NDAC 
                   
                   
                   
               
               
                 4 
                 1% cystine + 
                 clear 
                 none 
                 no 
               
               
                   
                 5% NDAC 
                   
                   
                   
               
               
                 5 
                 0.5% cystine 
                 precipitate 
                 none 
                 no 
               
               
                 6 
                 0.5% cystine + 
                 clear 
                 none 
                 no 
               
               
                   
                 2% NDAC 
                   
                   
                   
               
               
                 7-A 
                 0.25% cystine 
                 precipitate 
                 none 
                 no 
               
               
                 8 
                 0.25% cystine + 
                 clear 
                 none 
                 no 
               
               
                   
                 1% NDAC 
                   
                   
                   
               
               
                 9-A 
                 0.5% cystine  b   
                 precipitate 
                 none 
                 no 
               
               
                 10 
                 0.5% cystine + 
                 clear 
                 none 
                 no 
               
               
                   
                 2% NDAC  b   
                   
                   
                   
               
               
                 11-B 
                 1% cystine + 
                 clear 
                 strong 
                 yes 
               
               
                   
                 4% NACys 
                   
                 sulforous 
                   
               
               
                 12-C 
                 1% cystine + 
                 precipitate 
                 strong 
                 yes 
               
               
                   
                 4% DEC 
                   
                 sulforous 
                   
               
               
                   
               
               
                   a  Cystine slowly begins to precipitate after 3 weeks. 
               
               
                   b  Experiment performed using Epilife ™ cell culture media instead of water or 0.775 M 
               
               
                 NaOH. 
               
            
           
         
       
     
     Samples marked by alphabetical characters (A through C above) were outside the scope of the invention. Numerically marked samples (without a letter following them) were within the scope of the invention. Samples-A were a positive control as they employed different concentrations of cystine alone. 
     The Table above shows the effect of NDAC, NACys and DEC on cystine crystallization and sulforous odor formation. Example 1 shows that cystine (1% by weight) is insoluble in aqueous solution containing 0.775 M NaOH that has been neutralized with HCl to pH 7.0. Addition of NDAC between 3.5%-5% (on a molar basis relative to cystine—Examples 2-4) to the cystine (1%) solution prevents crystallization of cystine and generates no sulforous odor up to 4 months, albeit at 3.5:1 NDAC:cystine molar ratio, cystine begins to crystallize after 3 weeks. Maintaining a 4:1 NDAC:cystine molar ratio but decreasing the cystine concentration to 0.5% or 0.25% (by weight) does not change the appearance or odor profile (Examples 5-8 versus Example 3). Changing the solution medium from water to cell culture media using 0.5% cystine does not change the appearance or odor profiles (Examples 9-10 versus Examples 5-6). Addition of NACys (4%—Example 11) to the cystine (1%) solution prevents crystallization of cystine but generates strong sulforous odor and some disproportionation to H 2 S occurs after 2 weeks. In contrast, addition of DEC (4%—Example 12) to the cystine (1%) solution does not prevent cystine crystallization, generates strong sulforous odor and some disproportionation to H 2 S occurs after 2 weeks. 
     As can be seen from the Table above, these results clearly and unexpectedly demonstrate the significant benefits of NDAC on preventing cystine crystallization above 3.5:1 NDAC:cystine mol % ratio, in water solutions containing 0.25-1% cystine or cell culture media containing 0.5% cystine, with no sulforous odor generated and further highlights the utility of such ingredient in formulations containing cystine for personal care use. 
     Therefore, it follows from the data above, that, as a result of solubilizing cystine, so it can convert to GSH, less cystine may be used in a composition. Using less cystine and/or replacing some of it with NDAC alleviates the solubility problems posed by cystine in efforts to include large amounts in personal care compositions. 
     Example II 
     Personal care formulations according to the present invention are illustrated in the Tables below. All numbers in the Tables represent weight % in the composition. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Oil-in-water formulations, lotions, and creams 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 OW-1 
                 OW-2 
                 OW-3 
                 OW-4 
                 OW-5 
               
               
                   
               
               
                 Water 
                 To 100 
                 To 100 
                 To 100 
                 To 100 
                 To 100 
               
               
                 Glycerine 
                  0-40 
                  1-40 
                 1-5 
                  1-10 
                  1-40 
               
               
                 Propylene glycol 
                 0-5 
                   
                 0-5 
                   
                   
               
               
                 Butylene glycol 
                 0-5 
                   
                 0-5 
                 0-5 
                   
               
               
                 Carbomer 
                 0-2 
                 0.03-1    
                   
                   
                   
               
               
                 Ammonium Acryloyl dimethyl 
                 0-1 
                   
                 0.03-1    
                   
                 0.01-1    
               
               
                 taurate/VP copolymer 
                   
                   
                   
                   
                   
               
               
                 Styrene/Acrylates copolymer 
                 0-1 
                   
                 0.01-1    
                   
                   
               
               
                 Xanthan Gum 
                 0-1 
                   
                   
                   
                 0.01-1    
               
               
                 EDTA 
                 0.01-0.01 
                 0.01-0.01 
                 0.01-1    
                 0.01-1    
                 0.01-1    
               
               
                 Preservative 
                 0.02-2    
                 0.02-2    
                 0.02-2    
                 0.02-2    
                 0.02-2    
               
               
                 Titanium oxide 
                  0-10 
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Colorant/Pigment 
                 0-5 
                 0-5 
                 0-5 
                 0-5 
                 0-5 
               
               
                 Triethanol amine/Sodium 
                 0-3 
                 0.01-3    
                 0.01-3    
                 0.01-3   
                 0.01-3    
               
               
                 Hydroxide/potassium 
                   
                   
                   
                   
                   
               
               
                 Hydroxide 
                   
                   
                   
                   
                   
               
               
                 Stearic acid 
                 0-5 
                 0.01-5    
                 0.01-5    
                 0.01-5    
                 0.01-5    
               
               
                 Isopropyl Myristate 
                  0-10 
                 0.01-10   
                   
                   
                   
               
               
                 Capric/Caprylic Triglyceride 
                  0-10 
                 0.01-10   
                   
                   
                   
               
               
                 C12-C15 alkyl benzoate 
                  0-10 
                   
                   
                   
                 0.01-10   
               
               
                 Mineral oil 
                  0-10 
                   
                   
                 0.01-10   
                   
               
               
                 Glyceryl stearate 
                 0-5 
                 0.01-5    
                   
                   
                   
               
               
                 Steareth-2 
                 0-5 
                   
                 0.01-5    
                   
                 0.01-5    
               
               
                 Steareth-21 
                 0-5 
                   
                 0.01-5    
                   
                   
               
               
                 Peg 100 Stearate 
                 0-5 
                   
                   
                 0.01-2    
                 0.01-5    
               
               
                 Potassium Cetyl Phosphate 
                 0-5 
                   
                   
                 0.01-2    
                   
               
               
                 Tween20 
                 0-5 
                   
                   
                   
                 0.01-5    
               
               
                 Cetyl alcohol 
                 0-4 
                 0.01-4    
                   
                 0.01-4    
                   
               
               
                 Dicaprylyl carbonate 
                 0-5 
                   
                 0.01-5    
                   
                   
               
               
                 Ethyl hexyl methoxycinnamate 
                 0-6 
                 0.01-6    
                   
                   
                   
               
               
                 Butyl 
                 0-3 
                 0.01-3    
                   
                 0.01-3    
                 0.01-3    
               
               
                 Methoxydibenzoylmethane 
                   
                   
                   
                   
                   
               
               
                 Ensulizole 
                 0-4 
                   
                   
                   
                 0.01-4    
               
               
                 Octinoxate 
                   0-7.5 
                   
                   
                   
                   
               
               
                 Octisalate 
                 0-5 
                   
                   
                 0.01-5    
                 0.01-5    
               
               
                 Octocrylene 
                  0-10 
                   
                   
                 0.01-10   
                 0.01-10   
               
               
                 Homosalate 
                  0-10 
                   
                   
                 0.01-10   
                   
               
               
                 Dimethicone 
                  0-10 
                 0.01-10   
                 0.01-10   
                   
                   
               
               
                 Cyclomethicone 
                  0-15 
                   
                 0.01-15   
                   
                   
               
               
                 Niacinamide 
                 0-5 
                 0-5 
                 0-5 
                 0-5 
                 0-5 
               
               
                 Fragrance 
                 0-2 
                 0-2 
                 0-2 
                 0-2 
                 0-2 
               
               
                 Glutamine/Sodium PCA 
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
                   
               
               
                 Glycine 
                   
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Cystine 
                 0.001-2    
                 0.001-2    
                 0.001-2    
                 0.001-2     
                 0.001-2    
               
               
                 NDAC 
                 0.001-3    
                 0.001-3    
                 0.001-3    
                 0.001-3     
                 0.001-3    
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE II 
               
             
            
               
                   
               
               
                 Water-in-oil topical lotions or creams 
               
            
           
           
               
               
               
               
               
            
               
                   
                 WO-1 
                 WO-2 
                 WO-3 
                 WO-4 
               
               
                   
               
               
                 Water 
                 To 100 
                 To 100 
                 To 100 
                 To 100 
               
               
                 Glycerine 
                  0-70 
                  1-70 
                  1-70 
                   
               
               
                 Propylene glycol 
                 0-5 
                   
                   
                 0.01-5    
               
               
                 Butylene glycol 
                 0-5 
                   
                 0.01-5    
                 0.01-5    
               
               
                 Disteardimonium Hectorite 
                 0.01-1    
                 0.01-1    
                   
                   
               
               
                 EDTA 
                 0.01-.01  
                 0.01-1    
                 0.01-1    
                 0.01-1    
               
               
                 Preservative 
                 0.02-2    
                 0.02-2    
                 0.02-2    
                 0.02-2    
               
               
                 TiO2 
                  0-10 
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Colorant/pigment 
                 0-5 
                 0-5 
                 0-5 
                 0-5 
               
               
                 TEA/Sodium 
                 0-3 
                 0.01-3    
                 0.01-3    
                 0.01-3    
               
               
                 Hydroxide/potassium 
                   
                   
                   
                   
               
               
                 Hydroxide 
                   
                   
                   
                   
               
               
                 Stearic acid 
                 0-5 
                 0.01-5    
                   
                   
               
               
                 Isopropyl Myristate 
                  0-10 
                   
                   
                   
               
               
                 Capric/Caprylic Triglyceride 
                  0-10 
                   
                 0.01-10   
                   
               
               
                 C12-C15 alkyl benzoate 
                  0-10 
                   
                   
                 0.01-10   
               
               
                 Mineral oil 
                  0-10 
                   
                   
                   
               
               
                 Glyceryl stearate 
                 0-5 
                   
                   
                   
               
               
                 Dimethicone copolyol 
                 0-5 
                 0.01-5    
                 0.01-5    
                   
               
               
                 Cetyl PEG/PPG-10/1 
                 0-5 
                   
                   
                 0.01-5    
               
               
                 Dimethicone 
                   
                   
                   
                   
               
               
                 Steareth-2 
                 0-2 
                   
                   
                   
               
               
                 Sucrose Distearate 
                 0-2 
                 0.01-2    
                   
                   
               
               
                 Cetyl alcohol 
                 0-2 
                 0.01-2    
                 0.01-2    
                   
               
               
                 Ethyl hexyl methoxycinnamate 
                 0-6 
                 0.01-6    
                   
                   
               
               
                 Butyl 
                 0-3 
                 0.01-3    
                 0.01-3    
                 0.01-3    
               
               
                 Methoxydibenzoylmethane 
                   
                   
                   
                   
               
               
                 Ensulizole 
                 0-4 
                   
                 0.01-4    
                   
               
               
                 Octinoxate 
                   0-7.5 
                   
                   
                   
               
               
                 Octisalate 
                 0-5 
                   
                 0.01-5    
                 0.01-5    
               
               
                 Octocrylene 
                  0-10 
                   
                 0.01-10   
                 0.01-10   
               
               
                 Homosalate 
                  0-10 
                   
                   
                 0.01-10   
               
               
                 Dimethicone 
                  0-10 
                   
                 0.01-10   
                 0.01-10   
               
               
                 Cyclomethicone 
                  0-40 
                 0.01-40   
                   
                 0.01-10   
               
               
                 Caprylyl methicone 
                  0-10 
                 0.01-10   
                   
                 0.01-10   
               
               
                 Dimethicone crosspolymer 
                  0-90 
                 0.01-90   
                 0.01-90   
                   
               
               
                 C30-C45 alkyl cetearyl 
                   
                   
                   
                 0.01-90   
               
               
                 dimethicone crosspolymer 
                   
                   
                   
                   
               
               
                 Glycolic acid 
                  0-10 
                 0.01-10   
                   
                   
               
               
                 KCl 
                 0-5 
                 0.01-5    
                 0.01-5    
                 0.01-5    
               
               
                 Iacinamide 
                 0-5 
                 0.01-5    
                 0.01-5    
                 0.01-5    
               
               
                 Fragrance 
                 0-2 
                 0-2 
                 0-2 
                 0-2 
               
               
                 Glutamine/Sodium PCA 
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Glycine 
                   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Cystine 
                 0.001-2    
                 0.001-2     
                 0.001-2     
                 0.001-2     
               
               
                 NDAC 
                 0.001-3    
                 0.001-3     
                 0.001-3     
                 0.001-3     
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE III 
               
             
            
               
                   
               
               
                 Vanishing Creams 
               
            
           
           
               
               
               
               
               
            
               
                   
                 VC-1 
                 VC-2 
                 VC-3 
                 VC-4 
               
               
                   
               
               
                 Water 
                 To 100 
                 To 100 
                 To 100 
                 To 100 
               
               
                 Glycerine 
                 0-5 
                 0.01-5    
                 0.01-5    
                   
               
               
                 EDTA 
                 0.01-.01   
                 0.01-.01  
                 0.01-.01  
                 0.01-.01  
               
               
                 Preservative 
                 0.02-2    
                 0.02-2    
                 0.02-2    
                 0.02-2    
               
               
                 TiO2 
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Colorant/pigment 
                 0-5 
                 0.01-5    
                 0.01-5    
                   
               
               
                 TEA/Sodium Hydroxide/potassium 
                 0-3 
                 0.01-3    
                 0.01-3    
                 0.01-3    
               
               
                 Hydroxide 
                   
                   
                   
                   
               
               
                 Stearic acid 
                  0-30 
                 0.01-30   
                 0.01-30   
                 0.01-30   
               
               
                 Isopropyl Myristate 
                 0-5 
                 0.01-10   
                 0.01-10   
                   
               
               
                 C12-C15 alkyl benzoate 
                 0-5 
                   
                   
                 0.01-10   
               
               
                 Brij 35 
                 0-5 
                 0.01-5    
                   
                   
               
               
                 Tween40 
                 0-5 
                   
                   
                 0.01-5    
               
               
                 Cetyl alcohol 
                 0-2 
                 0.01-2    
                 0.01-2    
                   
               
               
                 Ethyl hexyl methoxycinnamate 
                 0-6 
                 0.01-6    
                 0.01-6    
                   
               
               
                 Butyl Methoxydibenzoylmethane 
                 0-3 
                 0.01-3    
                 0.01-3    
                 0.01-3    
               
               
                 Ensulizole 
                 0-4 
                   
                   
                 0.01-4    
               
               
                 Octisalate 
                 0-5 
                   
                   
                 0.01-5    
               
               
                 Octocrylene 
                  0-10 
                   
                 0.01-10   
                 0.01-10   
               
               
                 Dimethicone 
                 0-5 
                 0.01-5    
                   
                   
               
               
                 Cyclomethicone 
                 0-5 
                   
                   
                 0.01-5    
               
               
                 Dimethicone crosspolymer 
                 0-4 
                   
                   
                 0.01-4    
               
               
                 Niacinamide 
                 0-5 
                 0.01-5    
                 0.01-5    
                 0.01-5    
               
               
                 Hydroxystearic acid 
                 0-5 
                 0.01-5    
                 0.01-5    
                 0.01-5    
               
               
                 Fragrance 
                 0-2 
                 0-2 
                 0-2 
                 0-2 
               
               
                 Glutamine/Sodium PCA 
                 0.01-10   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Glycine 
                   
                 0.01-10   
                 0.01-10   
                 0.01-10   
               
               
                 Cystine 
                 0.001-2     
                 0.001-2     
                 0.001-2     
                 0.001-2     
               
               
                 NDAC 
                 0.001-3     
                   
                   
                   
               
               
                 NDAC 
                   
                 0.001-3     
                   
                   
               
               
                 NDAC 
                   
                   
                 0.001-3     
                   
               
               
                 NDAC 
                   
                   
                   
                 0.001-3