Background of the Invention Melanin is a pigment found in the skin which plays a key role in protecting the body from ultraviolet radiation. Melanin is produced in the form of granules called melanosomes within a type of cell called a melanocyte.

Melanosomes are transferred to a layer of keratin-producing cells near the outer surface of the skin known as keratinocytes. The greater the number of melanosomes transferred to keratinocytes, the darker the skin appears.

Occasionally alterations occur in this process whereby excessive darkening of the skin is observed. Such so-called"hyperpigmentation"can be associated with freckles, senile lentigo, lentigines, pregnancy, melasma, chloasma, post- inflammatory hyperpigmentation, sunburn, phototoxic reactions, and other conditions. While not usually life-threatening, hyperpigmentation is viewed as cosmetically undesirable and psychologically debilitating. The only treatment approved for lightening the skin in the United States is topical application of 1,4 benzenediol, also known as hydroquinone, which acts by reducing the number of melanosomes produced by melanocytes. Hydroquinone is sold in concentrations up to 2% without prescription, and in concentrations of 3-4% by prescription.

Although fairly effective, Hydroquinone preparations can cause side effects ranging from skin redness, burning and sensitization to paradoxical effects such as skin darkening. There is a need for new treatments for hyperpigmentation which are at least as effective as hydroquinone but are hydroquinone-free.

Summary of the Invention A method for lightening the skin is provided which comprises applying to

hyperpigmented areas of the skin a composition which includes: (1) Kojic acid and/or derivatives thereof, (2) an anti-oxidant and (3) a hydroxy acid and/or derivatives thereof. A composition for lightening the skin is also provided which includes: (1) Kojic acid and/or derivatives thereof, (2) an anti-oxidant and (3) a hydroxy acid and/or derivatives thereof.

Detailed Description of the Invention Kojic acid is a well known and commercially-available compound.

Dermally-available derivatives of Kojic acid may also be used, such as Kojic dipalmitate. A dermally-available derivative of Kojic acid is a compound that makes Kojic acid or a biologically active form of Kojic acid available in the skin.

Kojic acid and/or derivatives thereof may be employed in the composition in the range of about 1 to 25% w/w, and preferably between 2 and 10% w/w.

Anti-oxidants for use in the invention may include ascorbic acid (vitamin C) and/or derivatives thereof, especially Magnesium ascorbal phosphate; tocopherol (vitamin E), Tocopherol acetate, other esters thereof; butylated hydroxy benzoic acids and their salts; 6-hydroxy-2, 5, 7,8 tetramethylchroman-2- carboxylic acid (commercially available under the trademark TROLOX); gallic acid and its alkyl esters, especially propyl gallate; uric acid and its salts and alkyl esters; sorbic acid and its salts, the ascorbyl esters of fatty acids; amines, such as N, N-diethylhydroxylamine and amino-guanidine; sulfhydryl compounds, such as glutathione and N-acetyl cysteine; and dihydroxy fumaric acid and its salts. Such anti-oxidants may be used alone or in combination. The anti-oxidant component may be employed in the composition in a concentration sufficient to exhibit anti- oxidant activity in vivo; for example, in the case of ascorbic acid or magnesium ascorbyl phosphate, concentration range of about 1 to 25% should be employed, preferably between 5 and 10% w/w.

Hydroxy acids for use in the invention encompass the general class of organic compounds containing at least one hydroxy group and at least one carboxyl group, wherein at least one hydroxyl group is located on the alpha-or

beta-carbon atom. Typically, the hydroxy acid will have a single hydroxyl group (other than that associated with a carboxyl moiety), on the alpha-carbon atom, and may contain one, two or three carboxyl groups. Most typically, these compounds will have a basic structure of lower aliphatic compounds having from two to six carbon atoms.

The derivatives of these hydroxy acids most typically will involve derivatives related to carboxyl functionality, i. e., wherein the hydroxy or hydroxyl portion of the carboxyl moiety is substituted by metallic ions (to form salts), alkoxy groupings (to form esters), ammonium ions (to form ammonium salts), as well as other substitution reactions and products leading to formation of corresponding lactones, anhydrides or amides. However, the derivatives may also include reactions involving the alpha-hydroxyl group, most notably ketone formation, to form corresponding alpha-keto carboxyl acids.

Among the hydroxy acids and derivative compounds useful in the present invention are glycolic acid, glucuronic acid, galacturonic acid, gluconic acid, glucoheptonic acid,-hydroxybutyric acid,-hydroxyisobutyric acid,- hydroxyisocaproic acid,-hydroxyisovaleric acid, lactic acid, malic acid, muric acid, citric acid, saccharic acid, tartaric acid, tartronic acid, isocitric acid, dihydroxymaleic acid, dihydroxytartaric acid and dihydroxyfumaric acid.

Derivatives involving keto groups include keto acids and keto esters such as pyruvic acid, methyl pyruvate, ethyl pyruvate, isopropyl pyruvate, benzoylformic acid, methyl benzoylformate and ethyl benzoylformate. An example of a suitable beta hydroxyacid for use in the invention is salicylic acid.

The hydroxy acids and related compounds may be employed as free acids or esters, lactones, amides, anhydrides, inorganic metal salts, ammonium salts or salts created by reacting a hydroxy acid with an amino acid. Because of the natural presence of water-soluble acids in human skin, certain salts of these acids may convert, at least partially, to free acid form upon application. The hydroxyacid and/or derivatives thereof should be employed at a concentration of between about 1 and 25% w/w, and preferably between 2.0 and 10%.

The three components, together with appropriate carriers or vehicles, can be compounded into dermatologically useful cream, lotion, solution or gel preparations as follows: Example 1 Cream Ingredient % Cetearyl alcohol (and) Ceteareth-20 4.0 Mineral Oil 9. 0 Glyceryl stearate (and) PEG 100 Stearate 3.0 Vitamin E Acetate 2.5 Kojic Dipalmitate 4.2 Cetostearyl alcohol 1.5 Glycerin 2.0 Disodium EDTA 0.1 Lactic acid 7.5 Magnesium ascorbyl phosphate 9.5 Sodium or Ammonium hydroxide Q. S.

Preservative Q. S.

Deionized water Q. S.

The cream is prepared by combining the oil-phase ingredients in a mixing container and heating them to 70 degrees C. The water phase ingredients, except for the Lactic acid and Magnesium ascorbyl phosphate, are combined and heated to the same temperature. The two phases are then combined and cooled with constant mixing. At approximately 50 degrees the Lactic acid and ascorbate are dissolved. Preferably, due to the sensitivity of the ascorbate to elevated temperatures and oxidation in aqueous solvents, it may be advantageously packaged as a dry powder in a separate container which would accompany ajar of the cream. At time of dispensing or first use, the powder would be incorporated into the cream with a stirring rod where it would dissolve in the water phase.

Example 2 Lotion Ingredient % Glyceryl stearate (and) PEG 100 stearate 1.5 Glyceryl stearate and ceteth-20 1.5 Cetyl alcohol 1.0 Octyl 2 dodecanol 3.0 Caprylic/capric triglyceride 8.0 Cetearyl isononanoate 4.0 Dimethicone, 100 cst 0.5 Kojic dipalmitate 3.0 Glycerin 2.0 Disodium EDTA 0. 1 Xanthan gum 0.3 Magnesium aluminum silicate 1.0 Lactic acid 8. 0 Magnesium ascorbyl phosphate 10. 0 Sodium or Ammonium hydroxide Q. S.

Preservative Q. S.

Deionized water Q. S.

The lotion is prepared by combining the oil-phase ingredients in a mixing container and heating them to 75 degrees C. The water phase ingredients, except for the Lactic acid and Magnesium ascorbyl phosphate, are combined and heated to the same temperature. The two phases arc then combined and cooled with constant mixing. At approximately 45 degrees the Lactic acid and ascorbate are dissolved. Preferably, due to the sensitivity of the ascorbate to elevated temperatures and oxidation in aqueous solvents, it may be advantageously packaged as a dry powder in a separate container which would accompany a bottle of the lotion. At time of dispensing or first use, the powder would be added to the lotion and shaken where it would dissolve in the water phase.

Example 3 Solution Ingredient % Deionized water Q. S.

Vitamin E PEG 1000 Succinate 0.3 Propylene glycol 5. 0 Glycolic acid 5.0 Ascorbic acid 7.0 Kojic acid 3.0 Ethanol 16.0 Laureth-4 1. 0 Squalane 0.2 Sodium or Ammonium hydroxide Q. S.

Preservative Q. S.

The solution is prepared by combining the alcohol, laureth-4 and squalane and adding the resulting solution slowly with mixing to the aqueous solution of the other ingredients at room temperature. Preferably, due to the sensitivity of the kojic acid and ascorbate to oxidation in aqueous solvents, they may be advantageously packaged as a dry blended powder in a separate container which would accompany the bottle of the solution. At time of dispensing or first use, the powder would be added to the solution and shaken where it would dissolve in the hydro-alcoholic solvent carrier.

Example 4 Gel Ingredient % Deionized water Q. S.

Hydroxyethyl cellulose 0.3 Propylene glycol 5.0 Glycolic acid 2.0 N-Acetyl cysteine 1.0 Magnesium ascorbyl phosphate 5.0

Kojic acid 2. 0 Ethanol 20.0 Salicylic acid 1.0 Laureth-4 1.0 Squalane 0.2 Sodium or Ammonium hydroxide Q. S.

Preservative Q. S.

The gel is prepared by combining the alcohol, Salicylic acid, laureth-4 and squalane and adding the resulting solution slowly with mixing to the aqueous solution of the other ingredients at room temperature. Preferably, due to the sensitivity of the kojic acid, N-Acetyl cysteine and ascorbate to oxidation in aqueous solvents, they may be advantageously packaged as a dry blended powder in a separate container which would accompany the bottle of the solution. At time of dispensing or first use, the powder would be added to the gel and stirred or shaken where it would dissolve in the hydro-alcohol solvent carrier.

Example 5 The Melanoderm assay is an in vitro model of the human epidermis consisting of well differentiated, cultured human keratinocytes and melanocytyes.

This model can be used to evaluate the efficacy, stability and cytotoxicity of skin lightening agents.

After application of a skin lightening test preparation and L- Dihydroxyphenylalanine (L-DOPA) the Melanoderrn is incubated. The resultant changes in the formation of melanin are compared with a positive L-DOPA control without any of the test preparation. Any reduction in melanin formation of the test preparation-treated Melanoderrn compared with the control predicts skin lightening activity of the test preparation.

The following table summarizes reduction of melanin formation for test creams formulated as in Example 1 containing Kojic dipalmitate, Lactic acid and Magnesium ascorbyl phosphate individually and in combination, along with a commercially-available 4% Hydroquinone cream:

TABLE 1 Test Preparation % Melanin Reduction Kojic dipalmitate only 45% Lactic acid only 40% Magnesium ascorbyl phosphate only 33% Kojic dipalmitate + Lactic acid 52% Kojic dipalmitate + Magnesium ascorbyl phosphate only 48% Lactic acid + Magnesium ascorbyl phosphate only 45% Kojic dipalmitate + Lactic acid + Magnesium ascorbyl phosphate 65% Hydroquinone, 4% Cream 59% The results suggest the combination of Kojic derivative, hydroxy acid and ascorbate anti-oxidant produce an unexpectedly greater skin lightening effect than each agent used individually or in paired combination. Furthermore, the combination was at least as effective as a commercially-available Hydroquinone Cream.