Excerpt from Skin Lightening and Depigmenting Agents
Synonyms, Key Words, and Related Terms: cosmetic lightening, cosmetic depigmentation, cosmetics, skin bleaching, hyperpigmentation treatment, hyperpigmentation, depigmentation agents, depigmenting agents, topical depigmentation, topical lightening, topical depigmentation agents, topical lightening agents, hydroquinone, monobenzyl ether of hydroquinone, azelaic acid, kojic acid, mequinol, arbutin, paper mulberry, glabridin, licorice extract, Arctostaphylos patula, Arctostaphylos viscida, magnesium ascorbyl phosphate, laser depigmentation, intense pulsed light depigmentation, fractional photothermolysis
Depigmenting agents are commonly prescribed to treat disorders of hyperpigmentation. In this article, a review is presented of several notable depigmenting agents reported in the literature. Although some of these topical agents are available only in certain research institutions, a growing number of products can be used by physicians as part of an armamentarium for treating disorders of hyperpigmentation. Recent advances in the field of cosmetic dermatology have developed lasers as another modality for the treatment of hyperpigmentation.
A basic understanding of the pigmentation pathway is helpful prior to a discussion of various skin-lightening agents and their known mechanisms of action. The type and amount of melanin synthesized by the melanocyte and its distribution pattern in the epidermis determines the actual color of the skin. Melanin forms through a series of oxidative reactions involving the amino acid tyrosine and the enzyme tyrosinase.
The first step is the most critical because the remainder of the reaction sequence can proceed spontaneously at physiological pH. Here, tyrosinase converts tyrosine to dihydroxyphenylalanine (DOPA) and then to dopaquinone. Subsequently, dopaquinone is converted to dopachrome through auto-oxidation, and finally to dihydroxyindole or dihydroxyindole-2-carboxylic acid (DHICA) to form eumelanin (black-brown pigment). The latter reaction occurs in the presence of dopachrome tautomerase and DHICA oxidase. In the presence of cysteine or glutathione, dopaquinone is converted to cysteinyl DOPA or glutathione DOPA. Subsequently, pheomelanin, a yellow-red pigment, is formed.
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