Ascorbic acid. The stable ester of ascorbic acid (ascorbyl) is used in treating hyperpigmentation. It acts on the melanogenesis cascade, interacting with copper ions to reduce dopaquinone and block dihydrochinindol-2-carboxyl acid oxidation (22). When objective measures were used in a double-blind, randomized trial study to determine efficacy, ascorbic acid (Mg L-ascorbyl-2 phosphate) in a 10% cream base had an efficacy similar to that of hydroquinone in melasma patients (23). Subjective measurements favored hydroquinone. However, these data are limited, and larger studies should be done to verify its efficacy.
Retinoid monotherapy is conducted with tretinoin (all-trans-retinoic acid), which is formed from the oxidation of the aldehyde group of retinene to a carboxyl group. Tretinoin reduces epidermal pigment in a variety of pigmentary disorders (lentigines, melasma, pigmentation of aging, and PIH) in dark skinned people (24). Results are encouraging, but improvement can take from several months to one year (25).
Tazarotene, an acetylenic topical retinoid, produces good results in pigmented aging spots. Moderate to marked depigmenting effect occurs when used as a gel in a concentration of 0.1%.