Skin whitening refers to the practice of using chemical substances to lighten skin tone by lessening melanin concentration. Melanins are dark-coloured pigments produced by special skin cells called melanocytes. Whitening agents act at various levels of melanin production in the skin. Several of them are competitive inhibitors of tyrosinase, a key enzyme in melanogenesis. Certain others inhibit enzyme maturation or prevent transport of melanin-carrying granules from melanocytes to surrounding keratinocytes.

These melanin-inhibiting ingredients are used alone or in combination with a sunscreen or a retinoid in the form of topical lotions or gels. Several plant-derived and synthetic chemicals are being used in these treatments and are also being incorporated into skin care cosmetics. In medical literature, hydroquinone is considered the primary topical ingredient for inhibiting melanin production. It is used topically from 2% to 4% concentrations singly or in combination with tretinoin (0.05% to 0.1%). A powerful inhibitor of melanin, hydroquinone lightens skin tone by disrupting melanin pigmentation. At higher concentrations of 4%, it could be a skin irritant especially when used in combination with tretinoin.

Some alternative lighteners are natural sources of hydroquinone such as those listed below: