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 &#34;niacinamide&#34; 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 2  is alkyl containing from 1 to 4 carbon atoms, preferably CH 3 , and R 3  is alkyl containing from 4 to 10  carbon atoms, preferably C 6  H 13  or an alkoxyalkyl group of the type --R 4  --O--R 5  wherein R 4  is alkylene containing from 1 to 4 carbon atoms and R 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 8  H 17 . 
     These general classes of ultra-violet absorber will hereinafter be referred to a &#34;uv absorbers (a)&#34; and &#34;(b)&#34; 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: 
     Powder Absorbents 
     Magnesium silicate 
     Lanolin absorption base 
     Amorphous silica powder 
     Powder Binders and Carriers 
     Microcrystalline cellulose 
     Isostearyl neopentanoate 
     Polyacrylamide 
     Lauryl lactate 
     Precipitated silica 
     Talc 
     Chalk 
     Emollients 
     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 
     Propellants 
     Trichlorofluoro methane 
     Dichloro difluoro methane 
     Dichloro tetrafluoro ethane 
     Monochloro difluoro methane 
     Trichloro trifluoro ethane 
     Propane 
     Butane 
     Isobutane 
     (used singly or in admixture) 
     Solvents 
     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 
     Humectants 
     Glycerin 
     Sorbitol 
     Sodium 2-pyrrolidone-5-carboxylate 
     Soluble collagen 
     Dibutyl phthalate 
     Gelatin 
     Polyglycerogen 
     Ethoxylated (10-20 moles) glucose 
     Propoxylated (10-20 moles) glucose 
     Thickeners 
     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. 
     
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                    % by weight                                           
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Stearic acid          15.0                                                
Cetyl alcohol         0.5                                                 
CYASORB UV 531        0.4                                                 
GIVTAN F              1.0                                                 
Glycerol              1.0                                                 
Niacinamide           3.0                                                 
Isopropyl myristate   4.0                                                 
Glyceryl monostearate 1.0                                                 
Caustic Potash (17.8%)                                                    
                      2.8                                                 
Formalin              0.05                                                
Perfume               0.2                                                 
Distilled water       to 100                                              
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     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.