Artificial Skin Darkening Composition and Method of Using the Same

This invention relates to cation/carrier solvent systems useful in the formulation of skin darkening compositions.

In our present society, a glowing suntan is frequently equated with a healthy, athletic life style and the means to pursue it on a year-round basis. However, the acquisition of a natural tan may not only be time consuming but almost impossible for those very light skinned persons who tend to burn rather than tan. In addition, the deleterious effects of excessive exposure to sunlight are becoming more generally recognized. One of the most common methods for artificially inducing a suntan is to subject the body to the rays of an ultraviolet ray lamp. While this induces a tan similar to the sun, it has many of the same disadvantages as tanning by the sun since many of the deleterious effects of sunlight are due to its U.V. radiation component. For instance, the increasing incidence of skin cancer has been attributed to increased exposure to U.V. radiation from the sun.

For these and other reasons, there is a perceived need for topically applied materials which simulate the appearance of a tan and, at the same time, protect the skin from U.V. induced damage.

The first step in any attempt to find such a material is to identify the exact effect desired. A suntan is really a combination of a brown coloration resulting from increased melanin synthesis, and a red coloration resulting from mild erythema if the exposure has been kept in the prudent range.

The material should be non-toxic and non-irritating, easy to apply, and stable in dermatologically acceptable formulations. The color produced on the skin should last for several days and be resistant to run-off and wash-off.

While dihydroxyacetone, which has been widely commercialized as a skin tanning agent, produces a brown coloration, it suffers from a number of problems. As mentioned above, a natural suntan has a reddish tint due to erythema. One attempt to remedy this shortcoming in dihydroxyacetone compositions involves the addition of alloxan which yields a pinkish-red color with proteins and peptides. Some commercial dihydroxyacetone preparations have contained up to 50% alcohol. Such alcoholic preparations tend to dry the skin. To overcome this, attempts have been made to use "creamy bases" such as are found in hand and face lotions, and cold creams. But dihydroxyacetone decomposes if any amino groups are present in the cream with a resulting loss in tanning ability. This limits the number of such cosmetic bases that may be used. Finally, due to dihydroxyacetone's reactivity toward amino groups, the types and thus number of sunscreens which may be used in conjunction with it are limited. Due to the negative attributes of dihydroxyacetone, the search for other artificial tanning agents has continued.

We have discovered that aqueous solutions containing cuprous ion and either benzyl alcohol or 2,3-dihydroxybenzoic acid produce a golden brown color closely resembling the color of a natural suntan when applied to the skin. Furthermore, these compositions are effective at concentration ranges lower than those generally found in commercially available artificial "tanning" products.

We have found that skin darkening closely resembling the tanning produced by ultraviolet radiation can be duplicated by certain carrier solvent/copper cation systems.

The compounds comprising the active ingredients in the present invention consist of cuprous chloride and either benzyl alcohol or 2,3-dihydroxybenzoic acid in aqueous solution. Cuprous chloride disassociates in water giving Cu.sup.+ ions, which are believed to be the active species. This theory is supported by the observation that no enhancement in tanning ability is apparent if solid cuprous chloride is added to a solution already saturated with cuprous chloride. The range of Cu.sup.+ ion useful in our invention is from about 0.45 mg/ml to about 0.9 mg/ml, the latter representing a saturated solution. The other active ingredient can be either benzyl alcohol or 2,3-dihydroxybenzoic acid, and is thought to act as a carrier solvent for the Cu.sup.+ ion. For use in our invention, the percent of carrier solvent by volume should be between 2% and 4%, the latter representing a saturated solution.

It is preferred that the aqueous solution be saturated with respect to both the cuprous ion and the carrier solvent. As the concentration of active ingredients is decreased, a corresponding decrease will occur in the speed of tanning and in the intensity of color ultimately produced. Depending on how light the individual's skin is before treatment, it is possible to use systems where the concentrations of active ingredients are even lower than those set out above and still produce a slight coloration. The lower limits of 0.45 mg/ml for Cu.sup.+ and 2% for carrier solvent represent the point at which there is a distinguishable difference between a treated and an untreated site on the skin of an individual with a light complexion.

In its simplest form, our invention consists of cuprous chloride and either benzyl alcohol or 2,3-dihydroxybenzoic acid in water. If desired, it is also possible to employ our invention in conjunction with a pharmaceutically acceptable dermatologic base. By "dermatologic base" is meant a vehicle or carrier suitable for application to the skin, i.e., for topical or external use.

The dermatologic bases in which our carrier solvent/cation sytems may be employed include: hydro-alcoholic solutions, i.e. mixtures of water and alcohol containing up to 45% by weight of an alcohol in addition to any benzyl alcohol present; oil-in-water or water-in-oil emulsions including "creams" which are solid emulsions containing suspensions or solutions for external use, and "lotions" which are liquid suspensions or dispersions stabilized by the presence of suspending agents, surface active agents, or both and designed likewise for external application; and gels formed by the use of thickeners such as finely ground kaolin or clay, or other conventional thickeners such as hydroxyethylcellulose which are inert to the other substances in the composition. In addition to the above, cosmetic adjuvants can be added such as emulsifying agents, solvents, preservatives, buffers, perfumes, and bodying materials which confer on the product a desired consistency rendering it adaptable to topical application. It is also possible to dispense the product as an aerosol by packaging it with conventional propellant liquids.

In connection with "lotions", above, it was mentioned that surface active agents could be used in the practice of our invention. If desired, such surface active agents in an amount from about 0.05 to about 1 percent by weight of the composition can be added to the composition of the present invention.

Table I represents surface active agents which are operable in the practice of our invention, but should not be construed as being exclusive since any surface active agent inert to the other ingredients of the compositions may be employed.

While artificial tanning systems may be used by persons as a substitute for natural tanning, they may also be used by persons wishing to accelerate color development in the natural tanning process by using an artificial tanning composition in addition to exposing themselves to sunlight or other sources of ultraviolet radiation. Thus, it is of additional advantage to employ a system containing a conventional sunscreen in order to protect the skin from radiation that may produce dermal erythema. Our present invention satisfies that requirement and may be used with a variety of commercially available sunscreens. It is possible to use water soluble sunscreens as well as those having only limited solubility in water by employing a co-solvent such as ethanol in amounts up to 10% by volume in the final composition. In formulating emulsion bases, the sunscreen is added to the phase in which it is soluble. While almost any sunscreen will work, it is necessary in the practice of our invention to insure that no chemical reaction will occur between the particular sunscreen chosen and the tanning solution. The sunscreens of Table II may be employed in amounts from 0.1% to 3.0 % by weight of the composition.

p-aminobenzoic acid

sodium 2,2-dihydroxy-4,4-dimethoxy-5-sulfobenzophenone

amyl p-dimethylaminobenzoate

2-ethylhexyl p-dimethylaminobenzoate

glyceryl p-aminobenzoate

2-phenylbenzimidazolesulfonic acid

p-methoxycinnamic acid, diethanolamine salt

2-hydroxy-4-methoxybenzophenone

ethylhexyl p-methoxycinnamate

2-ethoxyethyl p-methoxycinnamate

The preferred concentration of sunscreen is approximately 0.1% by weight.

As stated previously, it is possible to dispense the product as an aerosol. Suitable propellants for the composition include, for example, hydrocarbons such as n-butane or isobutane present alone or in mixture thereof with propane; and halogenated hydrocarbons such as those sold under the trademark Freon, for example dichlorodifluoromethane, monochlorotrifluoromethane, trichlorotrifluoroethane, dichlorotetrafluorethane, etc.

The following specific examples are intended to illustrate the nature of this invention without acting as a limitation upon its scope.

Excess crystalline, anhydrous cuprous chloride is added with stirring to a previously prepared saturated solution of benzyl alcohol in water. The resulting saturated solution contains approximately 4 grams of benzyl alcohol and 90 mg of cuprous chloride per 100 ml. Within a short time (30 minutes to 2 hours) after applying this solution to the untanned skin, a golden-brown color closely resembling the color of a natural suntan appears. The color produced is not rubbed off by clothing, nor is it affected by normal washing and bathing. Over a period of several days, it gradually fades.

When applied to the skin, each of the compositions of Examples II-IX will result in the appearance of a golden-brown color closely resembling the color of a natural suntan within 30 minutes to 2 hours after application.