Patent Publication Number: US-2009234372-A1

Title: Epilation Method

Description:
The present invention relates to a method of epilation by emitting light flashes. Such a method can be used cosmetically to prevent hairs that are undesirable esthetically speaking from growing back. 
     Application FR 2 838 042 discloses a device for treatment by emitting light flashes that is adapted to permanent epilation of hairs of dark color. 
     The light energy transmitted to the hairs by the light flashes is transformed into heat. The temperature rise is sufficient to prevent hairs from growing back providing the hairs are dark in color. 
     When such a device is used with hairs that are light in color, e.g. light brown, red, blond, white, or not pigmented, the amount of light energy that is absorbed by the hairs is found to be insufficient. 
     Consequently, there remains a need to benefit from an epilation method that is adapted to hairs of light color. 
     U.S. Pat. No. 6,358,242 discloses a method of permanent epilation in which a photosensitive composition is applied to the skin after hairs have been removed, which composition penetrates into the follicles, and then the skin is irradiated using a laser diode in order to destroy the follicles. 
     In that method, it is necessary to massage the skin to enable the photosensitive composition to penetrate into the follicles, and then to eliminate the remaining photosensitive composition from the surface of the skin prior to irradiation. 
     The present invention provides a method of epilating hairs, in particular of light color, e.g. light brown, red, blond, white, or non-pigmented, the method comprising the steps consisting in:
         i) mechanically removing the hairs to be treated so as to cause blood masses to form in the follicular sacs of the removed hairs; and   ii) exposing the blood in contact with the follicular papillae of the removed hairs to at least one light flash so as to raise the temperature of the blood masses formed in this way.       

     Such a flash can raise the temperature of the mass of blood sufficiently to coagulate proteins of the follicular papillae from which hair regrowth originates, the mass of blood being in direct contact with the follicular papillae of the removed hairs. 
     Light-colored hairs comprise hairs of lightness L in the CIE L*a*b* colorimetric coordinate system is greater than 20, better greater than 25. 
     At least one treated hair may have a diameter as measured outside (away from) lying in the range 25 micrometers (μm) to 50 μm. At least one treated hair may present an implantation depth lying in the range 1 millimeter (mm) to 5 mm. 
     The method of the invention makes it possible to avoid hairs of light color growing back. 
     The method may be implemented in a plurality of sessions, prior to permanent epilation being achieved. 
     Steps i) and ii) may be repeated at least once after a time interval of at least 3 weeks. 
     Independently or in combination with the above, the invention also provides a method of epilation, in particular for strongly pigmented skin, the method including the step consisting in:
         exposing skin, in particular strongly pigmented skin, that has been subjected to mechanical removal of hairs so as to cause blood masses to form in the follicular sacs of the removed hairs, to at least one light flash so as to raise the temperature of the blood masses as formed in this way.       

     A refrigerated gel may be applied to the skin prior to the exposure to the light flash. 
     The hairs may be of light color. 
    
    
     
       The invention can be better understood on reading the following detailed description of non-limiting implementations thereof, and on examining the accompanying drawing, in which: 
         FIG. 1  is a block diagram summarizing an implementation of the method of the invention; 
         FIGS. 2 and 3  are diagrammatic longitudinal section views of a hair implanted in skin, and then removed; and 
         FIG. 4  is a block diagram summarizing a variant of the method. 
     
    
    
       FIG. 1  shows the steps of a method in accordance with the invention suitable for epilating hairs of light color. 
     The method begins with mechanically removing hairs from the region to be treated in a first step  10 , and then after a waiting stage  20 , in exposure to at least one light flash in a step  30 . 
     The mechanical removal of the hairs may consist in taking hold of the hairs, and then exerting traction thereon, manually or by moving an appliance, as shown in  FIGS. 2 and 3 . 
     The hairs may be removed mechanically by means of a pair of tweezers, wax, or an electric epilator using rotary disks, for example. An electric epilator is sold under the trademark Epilady®. The hairs can be removed one at a time or several at once. 
     After the hair  1  shown in  FIG. 1  has been removed mechanically, the fibrous sac  3  that contained the bulb of the hair that has been removed fills with blood S during step  20 , as shown in  FIG. 3 . The blood mass that forms is in intimate contact with the follicular papilla  4  of the hair that has been removed and with the epithelial sheath  5 . 
     The temperature of this blood mass S can be raised using the light energy of the light flash in step  30  to a temperature that is high enough, e.g. greater than 70° C., better greater than 80° C., to coagulate the proteins of the follicular papilla from which hair regrowth originates. 
     Waiting step  20  may have a duration that lies in the range 1 minute (min) to 10 min, for example, in particular in the range 2 min to 8 min, better in the range 3 min to 6 min. 
     Step  30  of exposure to at least one light flash can be performed by means of a flash lamp. The follicular papillae of the hairs that have been removed are subjected to a rise in temperature following the flash(es). Emitting a plurality of flashes at lower power can be preferable to emitting a single flash at higher power with certain phototypes in order to avoid raising the temperature of the skin. 
     The light flash(es) may be of a duration lying in the range 5 milliseconds (ms) to 100 ms, or in the range 10 ms to 90 ms, better in the range 20 ms to 80 ms. 
     When using a single flash, its duration lies for example in the range 5 ms to 100 ms with energy density lying in the range 10 joules per square centimeter (J/cm 2 ) to 40 J/cm 2 , better in the range 5 J/cm 2  to 30 J/cm 2 . 
     When using a succession of flashes, each flash is of a duration lying in the range 5 ms to 20 ms, with energy density in the range 2 J/cm 2  to 20 J/cm 2 ; the number of flashes lies for example in the range 2 to 10; the interval between flashes lies for example in the range 1 ms to 20 ms. The pulse train may thus last for 5 ms to 300 ms. 
     The emitted light spectrum may be adapted to the absorption spectrum of blood, and in particular of hemoglobin. The light spectrum received by the skin may present a peak in the range 450 nanometers (nm) to 650 nm, for example. 
     At least one filter may be used to filter the light emitted by the flash lamp in order to obtain the desired spectrum. Ultraviolet light having a wavelength shorter than 400 nm is preferably filtered out. 
     Step  30  may be performed by means of a hand tool comprising a light guide advantageously made of a material that conducts heat, e.g. sapphire. 
     It is possible to press the hand tool lightly against the skin while emitting flashes so as to expel hemoglobin from the zone treated during epilation. 
     In a variant implementation, shown in  FIG. 4 , a layer of gel is applied to the skin in a step  40  preceding the emission of the light flash(es). 
     The gel may present a high refractive index, e.g. lying in the range 1.2 to 1.6. The gel may be refrigerated before being applied to the skin, in particular with strong pigmentation, i.e. when the phototype of the skin is IV, V, or VI in the Fitzpatrick classification. 
     By way of example, the gel may be applied manually during waiting step  20 . 
     By way of example, the initial temperature of the gel may be less than or equal to 10° C., e.g. lying in the range 2° C. to 5° C. 
     The term “comprising a” should be understood as being synonymous with “comprising at least one” unless specified to the contrary.