Skin whitening, also known as skin lightening and skin bleaching, refer to the practice of using chemical substances in an attempt to lighten the skin or provide an even skin color by reducing the melanin concentration in the skin. Several chemicals have been shown to be effective in skin whitening, while some have proven to be toxic or have questionable safety profiles.Efforts to lighten the skin date back to at least the 1500s in Asia. While a number of agents such as kojic acid and alpha hydroxy acid are allowed in cosmetics in Europe a number of others such as hydroquinone and tretinoin are not.
Areas of increased pigmentation such as moles may be depigmented to match the surrounding skin. In cases of vitiligo, unaffected skin may be lightened to achieve a more uniform appearance. Effective agents for specific areas include corticosteroids, tretinoin, and hydroquinone. These agents however are not allowed in cosmetics in Europe due to concerns of side effects.Attempts to whiten large areas of skin may also be carried out by certain cultures. This may be done for reasons of appearance, politics, or economics.
Melanin is the main substance responsible for the color of the skin. Melanin in synthesized in melanosomes which are organelles produced in melanocytes, cells dedicated to this function that are present in the skin, hair follicles, and other structures of the body. The synthesis of melanin, also called “melanogenesis” and “melanization”, involves a chain of enzyme-catalyzed chemical reactions and non-enzyme-catalyzed reactions.
Melanosomes along with the melanin they contain are transferred from melanocytes to keratinocytes when keratinocytes are low in the epidermis. Keratinocytes carry the melanosomes with them as they move towards the surface. Keratinocytes contribute to skin pigmentation by holding the melanin originated in melanocytes and inducing melanogenesis through chemical signals directed at melanocytes.