Skin Lightening Composition and Method

The invention relates to skin cosmetic compositions which have a lightening effect on the skin.

In British Pat. No. 1,370,236 there is described a composition intended for application to the skin which contains niacin as a skin lightening agent. The method by which niacin acts to effect skin lightening is postulated as being a retardation of melanin dispersion or distribution into the epidermis.

We have now discovered that niacinamide and compounds releasing niacinamide on the skin can also act as skin lightening agents, it being apparent that niacinamide probably acts by a mechanism similar to that of niacin, although it does not appear to exhibit any unpleasant skin flushing reaction due to vasodilation of the peripheral blood vessels such as has been observed with niacin.

Furthermore, we have found that niacinamide is easier to formulate into compositions for application to the skin than is niacin, and also that niacinamide is more readily absorbed by the skin than is niacin.

It is accordingly one object of the invention to provide an improved cosmetic composition which is capable of lightening the skin.

In contrast, certain skin compositions have also been formulated for the purpose of maintaining the colour of skin against darkening following exposure to ultra-violet light; these compositions have generally been based on materials which deflect and scatter incident ultra-violet light of the wavelength which produces burning and tanning of the skin, or which absorbs this light.

It will be appreciated that sunburn, melanogenesis, and pigmentation of the skin are closely associated responses to irradiation by the erthemogenic spectrum. The photobiological changes that cause erythema also lead to melanogenesis and increased pigmentation. The so-called erythemogenic spectrum is generally considered to include wavelengths between 290 and 320 nm, with peaks at 297 or 300 - 207 nm. Light of wavelengths greater than 320 nm is thought to produce erythema.

The increase of melanin pigment that follows exposure of skin to solar radiation or ulatra-violet light from artificial sources involves two distinct photobiological processes:

(i) immediate pigment darkening of performed pigment without induction of erythema, and

(ii) the primary melanization involving induction of erythema, formation of new pigment and its dispersion.

The wavelengths which lie in the range of 320-420 nm with a broad maximum at 420 nm are responsible for the immediate pigment darkening in skin of preformed pigment without induction of erythema. Primary melanisation is most effectively initiated by wavelengths shorter than 320 nm.

It is accordingly a further object of the invention to provide an improved composition for topical application to the skin which not only lightens the skin but which also imparts protection from the immediate pigment darkening and the primary melanization due to exposure to solar radiation, thus prolonging the lightening effect.

According to the invention, there is provided a cosmetic composition for lightening human skin following topical application thereto, which composition comprises a skin lightening amount of niacinamide or a precursor thereof which is capable of releasing niacinamide of the skin, and a sunburn or santan protective amount of an ultra-violet absorbing sunscreen together with a mutually compatible cosmetically acceptable vehicle.

Niacinamide is the amide of niacin which is also known as nicotinamide or pyridine-3-carboxylic acid.

An example of a niacinamide releasing compound is niacinamide ascorbate.

The amount of niacinamide in the composition either as the niacinamide itself or a precursor thereof which is capable of releasing niacinamide on the skin should be sufficient to lighten the skin when the composition is applied to a human subject. For the skin lightening effect to be apparent, the skin will normally be that of a dark skinned subject, for example of Indian, West Indian or Negroid origin. It may furthermore be necessary for the composition to be applied repeatedly to the same area of skin, for example daily for 2 weeks, before skin lightening becomes evident. Hence the amount of niacinamide or its precursor present in the composition which constitutes a skin lightening amount can vary from subject to subject.

We have found that for general purposes, the amount of niacinamide or its precursor should be from about 0.1% to about 10% by weight of the composition, preferably from about 0.5 to about 5%.

In the following description the term "niacinamide" will include niacinamide itself or a precursor thereof which is capable of releasing niacinamide on the skin unless stated otherwise.

The ultra-violet absorbing sunscreen is preferably an ultra-violet absorber absorbing in the rang of 290-320 nm, which provides burn prevention properties. Preferably, this ultra-violet absorber is urocanic acid and/or a compound of the following formula: ##STR1## where R.sup.2 is alkyl containing from 1 to 4 carbon atoms, preferably CH.sub.3, and R.sup.3 is alkyl containing from 4 to 10 carbon atoms, preferably C.sub.6 H.sub.13 or an alkoxyalkyl group of the type --R.sup.4 --O--R.sup.5 wherein R.sup.4 is alkylene containing from 1 to 4 carbon atoms and R.sup.5 is alkyl containing from 1 to 4 carbon atoms.

To endow the compositions with tanning prevention properties, an ultra-violet absorbing sunscreen having maximum absorption in the tanning ray region of the spectrum, viz. 320-360 nm can be used. Examples of such compounds have the following formula: ##STR2## where R is alkyl containing from 4 to 12 carbon atoms, preferably C.sub.8 H.sub.17.

These general classes of ultra-violet absorber will hereinafter be referred to a "uv absorbers (a)" and "(b)" respectively.

Of the foregoing examples, the preferred UV absorbers (a) are selected from urocanic acid, and 2-ethoxyethyl-p-methoxy-cinnamate available for example from Givaudin as GIVTAN F. For compositions having tanning prevention properties, 2-hydroxy-4-octyloxybenzophenone, available for example as CYASORB 531 from the American Cyanamic Company is the preferred uv absorber (b).

Niacinamide can be formulated together with urocanic acid, a uv absorber (a) or a uv absorber (b) or preferably with a mixture comprising at least one uv absorber which absorbs in each part of the spectrum as herein described.

The advantages of using niacinamide in association with a uv absorber in each of the ranges 290-230 nm and 320-360 nm, is that the resultant skin composition not only lightens the skin, but protects it from both tanning and burning rays.

Appropriate amounts of uv absorber (a) are from about 0.1 to about 4% by weight of the composition and of uv absorber (b) about 0.1 to about 4% by weight of the composition, and when urocanic acid is used, it can be from about 0.1 to about 10% by weight of the composition.

The vehicle which forms part of the cosmetic composition is one or more substances which are mutually compatible with the niacinamide and the sunscreen and which are also cosmetically acceptable in that they will not harm the skin. The vehicle can act as a diluent, dispersant or carrier for the other ingredients of the composition, and is therefore intended to ensure that they can be readily applied to and distributed evenly over the skin at an appropriate concentration.

The vehicles that can be used in compositions according to the invention can include water, powder absorbents, binders and carriers, and liquids such as emollients, propellants, solvents, humectants and thickeners. Examples of each of these types of vehicles are as follows:

Magnesium silicate

Lanolin absorption base

Amorphous silica powder

Microcrystalline cellulose

Isostearyl neopentanoate

Polyacrylamide

Lauryl lactate

Precipitated silica

Talc

Chalk

Stearyl alcohol

Glyceryl monoricinoleate

Glyceryl monostearate

Sulphated tallow

Propylene glycol

Mink oil

Cetyl alcohol

Stearyl stearate

Isopropyl isostearate

Dimethyl brassylate

Stearic acid

Isobutyl palmitate

Isocetyl stearate

Oleyl alcohol

Isopropyl laurate

Hexyl laurate

Decyl oleate

Di-isopropyl adipate

2-octadodecanol

Iso-cetyl alcohol

Myristyl ethoxymyristate

Cetyl palmitate

Dimethylpolysiloxane

Di-isopropyl adipate

Di-n-butyl sabacate

Di-isopropyl sebacate

Di-2-ethyl hexyl sebacate

2-ethyl hexyl palmitate

Isononyl isononanoate

Isodecyl isononanoate

Isotridecyl isononanoate

2-ethyl hexyl palmitate

2-ethyl hexyl stearate

Di-(2-ethyl hexyl) adipate

Di-(2-ethyl hexyl) succinate

Isopropyl myristate

Isopropyl palmitate

Isopropyl stearate

Butyl stearate

Glyceryl monostearate

Polyethylene glycols

Propylene glycol

Triethylene glycol

Lanolin

Castor oil

Acetylated lanolin alcohols

Acetylated lanolin

Petrolatum

Isopropyl ester of lanolin fatty acids

Mineral oils

Butyl myristate

Isostearic acid

Palmitic acid

Isopropyl linoleate

Cetyl lactate

Lauryl lactate

Myristyl lactate

Quaternised hydroxy alkyl aminogluconate

Decyl oleate

Isodecyl oleate Di-isopropyl adipate

2-ethyl hexyl palmitate

Isostearyl neo pentanoate

Myristyl myristate

Di-isopropyl adipate

Oleyl ethoxy myristate

Diglycol stearate

Ethylene glycol monostearate

Myristyl stearate

Isopropyl lanolate

Trichlorofluoro methane

Dichloro difluoro methane

Dichloro tetrafluoro ethane

Monochloro difluoro methane

Trichloro trifluoro ethane

Propane

Butane

Isobutane

(used singly or in admixture)

Ethyl alcohol

2-ethylhexanol

Ethylene carbonate

Propylene carbonate

Castor oil

Linear ethoxylated polymer of methanol

Ethylene glycol monoethyl ether

Diethylene glycol monobutyl ether

Diethylene glycol monoethyl ether

Propoxylated butanol

Propoxylated oleyl alcohol

Butyl stearate

Butyl myristate

Glycerin

Sorbitol

Sodium 2-pyrrolidone-5-carboxylate

Soluble collagen

Dibutyl phthalate

Gelatin

Polyglycerogen

Ethoxylated (10-20 moles) glucose

Propoxylated (10-20 moles) glucose

Gums

Starch

Colloidal silicon dioxide

Sodium polyacrylate

Tetra alkyl and/or trialkyl aryl ammonium smectites

Chemically modified magnesium aluminum silicate

Organically modified montmorillonite clay

Hydrated aluminium silicate

Fumed silica

Carboxy vinyl polymer

Sodium carboxymethyl cellulose

Hydroxyethyl stearate amide

Ethylene glycol monostearate

The quantity of vehicle employed can constitute the balance of the composition, or a smaller proportion than the balance, provided that the vehicle is capable of performing, if necessary in admixture with other vehicles, its function as herein defined. One of the embodiments of the invention provides for a vehicle containing from about 1 to about 50 percent by weight of an emollient; and from about 10 to about 70 percent by weight of water.

Compositions according to the invention can be prepared for topical application to the skin in the form of conventional product types such as creams, lotions, ointments and aerosol products.

The invention is further illustrated by reference to the following example of a cosmetic cream.

The skin lightening effect of compositions according to the invention has been demonstrated in clinical testing in human subjects against a placebo without any actives. The skin lightening effect is gradual and reversible -- the colour of the skin returning to normal a few weeks after discontinuing use of this cream. The composition based on the invention provides a safe and gradual means of obtaining a fairer complexion.