METHOD OF EXFOLIATING SKIN AND COSMETIC KIT

DESCRIPTION

The present invention refers to a cosmetic method and kit to treat skin. More particularly, the invention refers to a cosmetic method to promote exfoliation of outer layers of human epidermis, and to a kit of products suitable to carry out said method.

It is known that keratinized cells forming the stratum corneum of the epidermis are subject to continuous desquamation and are replaced by cells deriving from the basal layer of the epidermis by mitotic activity. The elements produced therein are in turn pushed toward the outer and more superficial layers by the formation of new cells underneath. While migrating to the surface, the cells of the epidermis produce keratin that accumulates within them until most of the metabolically active cytoplasm is replaced. Cells die, lose their nucleus and cytoplasmic organs, and eventually detach from epithelium as small scales that are lifeless cell residues. Such series of changes, called cytomorphosis of the malpighian cells, requires from 15 to 30 days, depending on the part of the body and other factors. Ideally, such cell migration and replacement at the surface of the epidermis takes place in a perfect way, so that the skin is kept smooth and fresh. However, such process is far from being perfect, therefore accumulation of dead cells at the surface of epidermis occurs, causing irregular appearance and spots that are particularly visible in the area of face. Detachment or desquamation of accumulations of dead cells, also known as exfoliation, can be improved by using exfoliating products and/or processes, which can promote the detachment of such dead cells and impart a cleaner and better looking appearance to skin.

In the scientific and patent literature there are disclosed many exfoliating methods, capable to exert a mechanical or chemical action on the skin, or a combination of thereof.

From GB 2318298 it is known to use an ultrasonic device that removes accumulations of dead cells by micro-movements of a blade.

From US 6447789 it is known a skin cleaning and exfoliating composition comprising a tripolyphosphate as active principle, particularly sodium tripolyphosphate, possibly additivated with nutritional compounds such as vitamins.

From WO 02/30387 it is known an exfoliating composition based on oat extract formulated with suitable carriers, dispersing agents, emollients and other ingredients both organic and inorganic.

From WO 03/013448 it is known a method to exfoliate skin based on the use of a phosphosugar, in particular mannose phosphate.

Although the methods described above, either of a mechanical or chemical nature, can be

effective, there remains a need for a skin cleaning and exfoliating method that is simpler and cheaper than known methods.

It is therefore an object of the present invention to provide a simple, cheap and effective method for a cosmetic treatment of skin, more particularly a method to clean and exfoliate skin.

A further object of the invention is to provide a kit of products ready to be used for carrying out a method to clean and exfoliate skin.

The above and further objects of the invention are achieved by a method to cosmetically treat skin, characterized by comprising the following steps: a) apply a soap onto the skin to be treated, in the presence of water; b) apply an effective amount of a dermatologically acceptable alum on said skin; c) rub said skin; d) rinse said skin.

An additional aspect of the invention is represented by a kit of products to carry out said method, characterized by comprising a soap and a dermatologically acceptable alum as active principles, said soap and said dermatologically acceptable alum being physically separated to allow for a sequential application onto the skin to be treated.

With the term "soap" it is meant a surfactant belonging to the particular class of anionic surfactants consisting of sodium or potassium salts of saturated or unsaturated fat acids. Typically, soaps for personal hygiene are prepared from high quality fats, such as coconut oil, palm oil, and olive oil, which have a fat acids content of up to about 80%. Such soaps may contain free fat acids, fat alcohols, glycerin, lanolin, cocoa-butter, almond-oil, wheat germ oil, and ethanolamines of fat acids, typically in amount from 1 and 10% by weight. Other ingredients that may be present are cosmetic dyes, essential oils, perfumes, polish agents such as titanium dioxide, honey, herb or camomile extracts, milk powder, abrasive agents, antioxidants, optical whiteners, chelating agents, preservatives and the like. Soaps can be hard (sodium salts) or soft (potassium salts), and can be sold in solid form (pieces or flakes), in semi-solid form (paste, cream, emulsion) and in liquid form (potassium salts with a fat acids content of 10-15%).

With the term "dermatologically acceptable alum" it is meant a double sulfate of aluminum and of a monovalent metal or ion M, of general formula M ₂ SO ₄ • A1 ₂ (SO ₄ ) ₃ • nH ₂ O, wherein M is an ion deriving from an alkali metal, silver or ammonium, provided that such alum be dermatologically acceptable, that is does not show harmful or undesired effects upon contact with human skin. Preferably M is sodium, potassium or ammonium, and n=24. More

preferably M is potassium. Potassium alum, also known as potash alum or simply "alum", is a substance that crystallizes as regular octahedron and is very soluble in water (at 5O ⁰ C 100 g of water dissolve up to 44,11 g of potassium alum). The formula of potassium alum is K ₂ SO ₄ • A1 ₂ (SO ₄ )3 • 24H ₂ O. Potassium alum has several practical applications, and it is known also as hemoastringent.

According to the present invention, alum can be used in the form of a solid bar made of compressed crystals or as a powder of crystals or as a water solution of crystals. As solid bar it can be advantageously fixed to an inert support, for easy application. As a powder of crystals it can be applied as such or sprayed onto the skin by means of a spray device or applied as powder contained in a flexible support such as a sponge, a cloth, a brush or the like, or as a water solution. The cosmetic method for treating the skin according to the invention comprises the steps of: a) apply a soap onto the skin to be treated, in the presence of water; b) apply an effective amount of a dermatologically acceptable alum on said skin treated with said soap; c) rub said skin; d) rinse said skin.

Step a) typically comprises the formation of a foam, on which alum is applied according to step b). Step c) comprises rubbing the skin, and is the step during which the biochemical action of the soap + alum composition combined with the mechanical action of rubbing brings about an effective cosmetic treatment of skin. Rubbing step c) is carried out in a time frame of from few seconds to few dozens of seconds, preferably from 5 to 30 seconds, more preferably from 10 to 15 seconds. During step c) it can be observed that foam formed during step a) disappears and solid particles are formed, which particles contain exfoliated keratinized epithelial cells mixed with soap. Such particles are removed by rinsing according to step d), with the final result that the skin is clean and aesthetically improved. When the skin to be treated is the skin of the face of a human, step b) of the method of the invention corresponds to the formation in situ of a facial mask, which is formed by protecting eyes and other sensitive areas, as usual in cosmetic treatments. Of course, the cosmetic treatment according to the invention can be carried out on any skin area, including the very sensitive ones. However, the method is particularly advantageous and effective in those areas of skin where thick or horny residues of keratinized cells are present.

The method of the invention can advantageously be carried out by using a kit in which the active principles consisting of soap and alum are provided in a form and amount suitable for a

combined sequential application. The kit may contain also additional cosmetic products, such as moisturizing creams, perfumes or the like, to be applied on the skin before or after the cosmetic method described above.

It has surprisingly been found that the combined sequential action of soap and alum, preferably potassium alum, allows to achieve an excellent cleaning of skin, since it exerts an effective exfoliating action on agglomerates of dead cells present on the surface of epidermis.

Such action results from a synergistic effect of soap and alum, substances that do not exhibit such effect when used separately, or exhibit it in much lesser degree than when used in combination and sequence.

The following examples illustrate some embodiments of the invention.

Example 1

Active principle 1: Bar of sodium soap Marseille type with 76% of fat acids.

Active principle 2: Rectangular bar of potassium alum sold by CO. MA. S.n.c, Viareggio,

(Italy).

Hands and arms were first soaped in the presence of water until a persistent foam is formed.

The soaped part was then rubbed with a bar of potassium alum. Rubbing was then continued for about 15 seconds. It was observed that the foam disappeared. The skin was then rinsed with plenty of water.

Example 2

Active principle 1: Bar of sodium soap Marseille type with 76% of fat acids.

Active principle 2: Commercial Potassium alum in powder form contained in a spray dispenser.

A facial mask was formed by soaping a face of a person until a persistent foam was formed, followed by a spray application of potassium alum in powder form on the soaped skin. The facial mask was then rubbed onto the skin with a wet sponge for 10 seconds. It was observed that the foam disappeared, then the mask was removed by rinsing with a cloth soaked in water.

Example 3

Active principle 1: liquid potassium soap with 14% of fat acids.

Active principle 2: Commercial Potassium alum in water solution form contained in a spray dispenser.

A facial mask was formed by soaping a face of a person until a persistent foam was formed, followed by a spray application of potassium alum in powder form on the soaped skin. The treated area was then manually rubbed for 30 seconds. It was observed that the foam

disappeared, then the mask was removed by rinsing with water.

Example 4 (comparison)

Use of active principle 1 only: Bar of sodium soap Marseille type with 76% of fat acids, formation of a layer of foam on hands and subsequent removal by rinsing.

Example 5 (comparison)

Use of active principle 2 only: Bar of commercial Potassium alum, rubbing of skin followed by rinsing with water.

Example 6 (comparison)

Active principle 1: Anionic surfactant sodium lauril sulfate, aqueous solution 10%.

Active principle 2: Commercial potassium alum, bar as in example 1.

A facial mask was formed by using sodium lauril sulfate until a foam is formed, then the treated area was rubbed with a bar of potassium alum. The mask was let in situ for 30 seconds, then it was removed by rinsing with water.

Evaluation of results

The effectiveness of the cosmetic method to treat skin according to the invention is shown by the results of the examples above, listed in Table 1 below. Effectiveness is determined with reference to the formation (YES) or not (NO) of solid particles containing agglomerates of exfoliated keratinized epithelial cells mixed with soap. After such particles were removed by rinsing, the skin was clean, smooth and aesthetically improved.

Table 1

It appears from Table 1 that the method characterized by the combined or sequential use of soap and potassium alum is highly effective in the exfoliation of skin. The combined use of the active principles is more effective than a separate use of each principle alone (comparison example 4 and 5), and it is also more effective than using surfactants other than soap (example 6).

The products and the cosmetic method to treat skin according to the invention were further investigated by means of an in vitro evaluation of the exfoliating and keratolytic effect on human 3D epidermis. The prediction of the exfoliating/keratolytic potential of tested products was made through cytotoxicity testing (MTT assay) on in vitro reconstituted human 3D skin, and through the morphological evaluation of the stratum corneum in histological sections . Cosmetic products are directly applied onto the human skin. Consequently, they should exhibit no or very low toxicity to the cells that form the skin. This is even more true for products to be applied in very sensitive areas, as the eye contour.

The assays performed in this investigation were carried out on a three-dimensional reconstructed human skin model, formed by human epidermal keratinocytes with a well- differentiated stratum corneum. This cell culture model is highly representative of the target tissue in vivo and it can be expected that biological effects of topical products will be predictive in these systems.

The objectives of these assays were to assess quantitatively the effects of the test materials and of the controls on skin cell survival (MTT assay), and qualitatively on the stratum corneum exfoliation.

The tested sample was a composition of a neutral soap and of potassium alum crystals applied together and with water on the skin for a superficial exfoliating effect. Products were tested at high concentration separately and together on the artificial skin for 20 minutes to simulate what happens in vivo. As controls, a strong keratolytic agent as glycolic acid at a concentration of 10 % and 30% for 20 minutes were used. A further control, as irritating agent, was a solution of 0.5% by weight of sodium laurel sulphate (SLS) applied for 20 minutes too. Sample preparation

The soap was applied after suspension in water at 10% by weight. Crystals of alum were dissolved in water at a concentration of 50% by weight. The products were applied together, at the same final concentrations as above. No meaningful differences were detected if the products were applied in a different sequence, as they immediately mix together and the final effect is due to the mix.

Glycolic acid was tested dissolved in water at 10 and 30% separately.

SLS was dissolved in water at 0.5%.

The cosmetic sample was tested as such, without further dilution and after stirring the suspension.

Normal saline alone was used as a negative control.

Cell model

3D epidermis models were purchased from Skinethic (Nice, France) and human keratinocytes were cultured up to the 16th day in a serum-free defined medium.

Treatment and exposure

10-20 mg of suspension of cosmetic sample were applied on two samples of epidermis; the exposure lasted 20 minutes. One of such samples was used to evaluate the skin morphology.

The other sample was kept for 20 minutes at 37 ⁰ C and 5% CO ₂ to perform the MTT cytotoxicity assay. It is clear that such tests were carried out at exposure times much longer than the normal ones, to stress the real condition of use.

MTT assay execution

The MTT assay is simple, accurate and generates reproducible results. The key component is

(3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) or MTT. This product is of yellowish colour in solution. Mitochondrial dehydrogenases of viable cells cleave the tetrazolium ring, leading to the formation of purple crystals which are insoluble in aqueous solutions. The crystals are re-dissolved in acidified isopropanol and the resulting purple solution is measured spectrophotometrically. An increase or decrease in cell number results in a concomitant change in the amount of formazan formed, indicating the degree of cytotoxicity caused by the test material.

MTT-medium was prepared as described by Mossman (Mossman, T. (1993). Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays. J. Immunol. Methods 65:55-63). After exposure of the cells to the test material, the cells were washed with PBS and exposed to the MTT-medium at 37 ⁰ C. At the end of the incubation period, the MTT-medium was removed and the cells received the MTT

Solubilization Solution. The plate was shaken on a rotatory plate shaker for 20-30 minutes, ensuring that all the crystals had dissolved from the cells and had formed a homogeneous solution. The absorbance was measured as described with background elimination.

The results are expressed in terms of viability:

% Viability = (OD treated cultures x 100) / (OD untreated control cultures)

Hystological section preparation and morphological documentation

After exposure to products and controls, the skin samples underwent dehydration through passages in growing concentrations of alcohol, and then embedded in paraffin for slices cut.

The slides were then rehydrated through alcohols passages and then coloured with ematossiline/eosine staining. Optic microscopy (Zeiss) images at magnitudo 800X were acquired through an Olympus digital photocamera (Table 3).

Results

Average cell survival after the exposure (20 minutes) was expressed as a percentage of non treated negative control values. The condition of use was simulated to allow a judgement on the specific toxic effect towards keratinocytes (Table 2).

Table 2

Morphological analysis

Table 3

Conclusions

Following the investigation described above, it appears that the tested samples of soap + potassium alum, when applied together on the artificial skin for 20', at the described concentrations, showed a moderate keratolitic effect and a good superficial exfoliating effect, without cytotoxic effects towards the skin cells.

In particular, the tested products, applied as described above, had a much lower cytotoxic/irritating effect than a conventional keratolytic agent as glycolic acid.