The benefits of AHAs have long been recognized. Sour milk [contains lactic acid (LA)] and sugarcane juice [contains glycolic acid (GA)] were applied to the face. In low concentrations, AHAs decreased corneocyte cohesion, leading to sloughing of dead cells and stimulation of new cell growth in the basal layer. In higher concentrations, they cause epidermilysis. AHAs have been reported to be effective in treating pigmentary lesions such as melasma, solar lentigines, and post-inflammatory hyperpigmentation. The mechanism of this effect might be due to epidermal remodeling and accelerated desquamation, which would result in quick pigment dispersion. GA and LA might work on pigmentary lesions not only by accelerating the turnover of the epidermis but also by directly inhibiting melanin formation by inhibiting tyrosinase in melanocytes (57). GA or LA (at doses of 300 or 500 mg/ml) inhibited melanin formation in similar dose-dependent manner, without affecting cell growth. The bioavailability of AHAs increases as the pH decreases (desirable pH 2.8-4.8), and they are the only peels that are time-dependent and can be neutralized easily.
A cream containing 4% HQ, 10% buffered GA, vitamins C and E, and sunscreen is safe and effective in the treatment of melasma (58). The addition of kojic acid to a gel containing 10% GA and 2% HQ further improves melasma (59). Javaheri et al. (55) concluded that a prepeel program of daily application of topical sunscreen (SPF-15) and 10% GA lotion at night for two weeks, followed by 50% GA facial peel with a duration of two, four and five minutes once every month for three consecutive months proved to be an effective treatment modality for melasma in Indian patients. The beneficial results achieved can be maintained with topical application of 10% GA and 2% HQ. There are hardly any side effects.