# A Survey of Preservatives Used in Cosmetic Products
## 1 Introduction  
Cosmetic products should not contain any microorganisms potentially harmful to human health throughout their entire period of use. The most common microorganisms found in contaminated cosme include _Pseudomonas aeruginosa_, _Staphylococcus aureus_, _Escherichia coli_, _Klebsiella oxytoca_, _Burkholderia cepacia_, _Enterobacter gergoviae_, _Candidata albicans_, and _Serratia marcescens_. Contaminated cosmetic products should not be sold or used. Microbial contamination can influence the color and smell of the cosmetic, and reduce the stability of products; in addition, toxins produced by microorganisms may cause allergies, skin irritations, and other undesirable reactions. Therefore, to inhibit the development of microorganisms and maintain the microbiological purity of the cosmetic during manufacture, packing and storage, thus ensuring the safety of its users, preservatives are added to cosmetic products [1; 2; 3; 4]. Preservatives are biologically active organic compounds and have strong effects on the growth and function of living cells and, as such, do not have a beneficial effect on the skin. They can be divided into several groups: carboxylic acids (aliphatic and aromatic) and their salts, alcohols (aliphatic and aromatic), parabens, compounds releasing free formaldehyde, isothiazoliones and other heterocyclic compounds, heavy-metal derivatives (organic mercury and silver compounds), and other compounds, like biguanides and quaternary ammonium salts [5]. The preservatives used in cosmetic products must meet several criteria. Among others, they should not be toxic and should not cause sensitization or irritation or damage the natural skin microbiome; also, they should not penetrate the skin or mucous membranesor affect the color and fragrance of the product. They should still exhibit activity against a broad spectrum of fungi and bacteria at the lowest possible concentrations. They are expected to be stable, to be resistant to light and oxygen, and not to react with other recipe ingredients. A good preservative should also have better solubility in the aqueous phase than the oil phase. The preservative system should be appropriately selected for the target group of the cosmetic [3; 5]. To be permitted for use in cosmetic ingredients, a preservative must comply with Annex V of the Regulation of the European Parliament and of the Council of the European Community (EC) No. 1223/2009 [6]. Annex V currently includes about 60 positions; however, it is constantly being updated. Recent changes to Regulation 1223/2009 include the prohibition of zinc pyrithione and restrictions on the use of salicylic acid and its salt. In addition, formaldehyde donors should be labeled with the warning \"releases formaldehyde\" when the total concentration of released HCHO in the finished product exceeds 0.001%. The list does not include preservatives of natural origin, such as essential oils or plant extracts. Permissible concentrations of preservatives listed in the above-mentioned regulations range from 0.0015% to 2.500%. Preservatives must be used in the minimum concentration that guarantees effective protection of the formulation but does not exceed the concentration at which they could cause irritation and undesirable side effects in users. Preservatives may cause hypersensitivity reactions and allergies, the most common symptom of which is allergic contact dermatitis, but contact urticaria has also been reported. They can also irritate the skin and mucous membranes [4; 7]. Thiomersal and formaldehyde donors have been found to have a negative impact on the human body. Methylisothiazol (MI) is banned for use in leave-on cosmetics due to its sensitizing effect. Also, quaternary ammonium compounds are irritating and toxic to mucous membranes and skin [7; 8; 9; 10]. The preservatives should be compatible with the other ingredients of the recipe. The presence of certain ingredients may reduce the effect of the preservative, while others may enhance its effect.