Adapalene is a retinoid-like compound that is chemically similar to vitamin A, and is used to reduce pimple and blackhead formation by stimulation of skin growth through modulation of cellular differentiation and keratinization of follicular epithelial cells. As a topical ointment, adapalene is used to treat acne vulgaris by assisting in keeping skin pores clear. Although the exact mechanism of action is unknown for adapalene, the drug does bind to specific retinoic acid receptors in the nucleus, but not in the cytoplasm, suggesting a regulatory genetic role. Although serious side effects are not likely to occur with topical application of adapalene, minor effects include burning, stinging, tingling, itching, redness, dryness, peeling, or skin irritation. Adapalene can increase the sensitivity of skin to ultraviolet radiation from sunlight, so prolonged exposure should be avoided by judicious use of sunscreens and protective clothing.