any one chemical compound that contains photosensitizing psoralen and reacts on exposure to ultraviolet light to increase the melanin in the skin. Naturally occurring psoralen photosynthesizers, such as 5- and 8-methoxypsoralen, are found in buttercups, carrot greens, celery, clover, cockleburs, dill, figs, limes, parsley, and meadow grass. Some psoralen-type photosensitizers produced as pharmaceutics are methoxsalen and trioxsalen; both are used to enhance skin pigmentation or tanning in the treatment of skin diseases, such as psoriasis and vitiligo. Such drugs are carefully administered to prevent oversensitization of the skin and other complications. Psoralen-type photosensitizers are also used in the manufacture of some perfumes, colognes, and pomades. Such chemicals cause unique skin reactions, such as berlock dermatitis, in some individuals. Oil of bergamot, extracted from the peels of small oranges grown in southern France and Italy, is a photosensitizing psoralen used as a tea flavoring and in perfumes.