CHENNAI, India—A new Indian review evaluated cosmetic skin-lightening ingredients, which are in big demand across Asia, for fairness (J Cosmet Sci. 2012;63(1):43-54). The mechanisms underlying pigmentation have been researched extensively and the knowledge is being updated regularly. This review serves to list the ingredients that are commercially available for that purpose and the modes of action through which the lightening is affected. Skin-lightening ingredients are also classified based on their sources; it is significant that far more botanicals have made the list than have synthesized compounds. Tyrosinase inhibition as a means of skin lightening is still the most reported method, followed by other methods such as Mitf inhibition, down regulation of MC1R activity, interference with melanosomal transfer and melanocyte loss.
Skin-lightening ingredients can be classified by their source, such as the classes to which they belong. The important classes are:
Chemical tyrosinase inhibitors: Hydroquinone is considered the gold standard but its use in cosmetics has lessened due to its adverse side effects from its cytotoxic nature. Arbutin, a naturally occurring beta,D-glycopyranoside derivative of hydroquinone, does inhibit tyrosinase but it doesn’t affect RNA synthesis as hydroquinone does. Kojic acid functions via chelation of copper at the active site of the enzyme tyrosinase, and acts as a free radical scavenger but it may induce allergic dermatitis. It’s also unstable in formulations and may cause discolorations.
Botanicals: Because botanicals, mainly from plants and algae, connote nature, they are more widely accepted. However, they can be highly unstable and incompatible within formulations. Examples include licorice extract, aloe leaf extract, cumin seed extract and more.
Antioxidants: Antioxidants reduce oxidation of tyrosine to DOPA quinine, in addition to acting in the melanogenesis pathway, reducing the synthesis of melanin. Phytic acid, glutathione and ubiquinone are popular antioxidants.
Vitamins—A, B, C, E: Vitamin A has been used for decades for the removal of spots in Kligman’s treatment. It induces exfoliation but side effects include burning and increased photosensitization. Vitamin B3 and B5 interferes in melanasome transfer leading to skin lightening and with the glycosylation of tyrosinase leading to depigmenting effects, respectively. Vitamin C deactivates UV-induced free radicals and decreases erythema, in addition to acting as a tyrosinase inhibitor. Vitamin E is the most important lipid-soluble antioxidant in the body and helps protect against inflammation and hyperpigmentation.
Peptides: Peptides reduce pigmentation through interaction with the protease-activated receptor 2 (PAR-2) of keratinocytes.
Alpha- and beta-hydroxyl acids and derivatives: These act as superficial chemical peels that target the stratum corneum to improve skin color and tone.
Researchers said although tyrosinase inhibition is still the most sought after mechanism skin lightening, newer pathways are being identified, such as interference with pathways affecting melanin synthesis and transfer. “The aspiration for light skin is on an upward curve and can be satisfied only when the cosmetic bottle fulfills the promise of fair skin," they concluded.
