For several years, there has been a growing interest, in the field of cosmetics, for depigmenting products: age spots (lentigo senile), chloasma, freckles, pigmentation spots that appear on mature skins after a prolonged exposure to the sun, are badly tolerated by affected people.
Fashion phenomena favouring light complexions in Asia and Africa are also factors in favour of the development of depigmenting products.
Melanin is a pigment synthesized by melanocytes which are specific cells of the epidermal basal layer.
Hyperpigmentations are often caused by hyperactivity of the melanocytes, eventually associated to an increase of their number.
Within melanocytes, oxidation reactions that lead to the formation of melanin are mainly catalyzed by tyrosinase. Resulting pigments are uniformly distributed over the epidermis surface, except when the mechanism is disrupted: melanin is then anarchically accumulated in some areas.
The depigmenting properties of some substances have been known for long: as soon as 1936, Oettel noticed a decrease of pigmentation among black cats hair which had been given hydroquinone (Hemsworth B. N. , J.Soc Cosmet. Chem., 1973, 24, 727-733).
Some substances showed a depigmenting action but cannot be used in cosmetic because of their toxicity (for example, mercury salts), of the cutaneous irritation they induce (mercaptoamines, oxidizing products such as hydrogen peroxide) or because of the excessive slowness of their action (ascorbic acid or ascorbic acid derivatives).
Other compounds such as phenolic derivatives, corticosteroids, analogs of vitamin A, some vegetal extracts are used as components in many depigmenting preparations now on the market.
However, these compounds show some side-effects: among phenolic derivatives, hydroquinone, which is an inhibitor of tyrosinase, induces quite a few secondary reactions (inflammatory reactions, burns, prickling sensations, irreversible dyschromia in spots); corticosteroids induce such secondary reactions and cannot be used in cosmetic; analogs of vitamin A (beta carotene, canthaxanthine) are able to block the melanocyte activity but the problem with these substances is making them to penetrate into the cells without being metabolized by the cell enzymes. Plant extracts, containing either arbutin (glucose hydroquinone) or flavonoids or also cinnamic derivatives, are also used as depigmenting agents but have a very slow action.
Generally speaking, the problem with these depigmenting agents of the prior art is that it will take at least a two months treatment before seeing the first results in vivo.