Hydroquinone is a hydroxyphenolic chemical. Hydroquinone has been the gold standard for treatment of disorders of hyperpigmentation for over 50 years. Hydroquinone possible mechanisms of action include the inhibition of the enzyme tyrosinase, inhibition of DNA and RNA synthesis, degradation of melanosomes, and destruction of melanocytes.
Hydroquinone has been used in concentrations of 1�10%. Its efficacy can be enhanced when combined with Vitamin C, retinoids, glycolic acid or salicylic acid to help increase absorption and cause exfoliation and stimulate skin renewal. 1%-2% Hydroquinone is available in over-the-counter products and 4% concentrations are available by prescription only. Treatment may take months to resolve. For hydroquinone to work effectively, it must be used long term. Sun exposure may cause hyper melanin production with darker skin type users.
Hydroquinone side effects include irritation, contact dermatitis, postinflammatory hyperpigmentation, nail discoloration, and hypopigmentation of normal skin surrounding the treated areas. Exogenous ochronosis, an irreversible disfiguring skin discorloration, has been reported in dark-skinned users due to long-term use of hydroquinone over large surface areas. Europe, South Africa, and most part of the world (except the United States) have banned the use of hydroquinone in cosmetics because of its potentially carcinogenic, mutagenic, and reproductive toxic effects.