What is "bergapten"

n. (context biochemistry English) 5-methoxypsoralen, a psoralen found in the essential oil of bergamot (where it is the cause of phototoxicity) and other citruses.

Bergapten (5-methoxypsoralen) is a psoralen (also known as furocoumarins) found in bergamot essential oil, in other citrus essential oils, and in grapefruit juice. It is the chemical in bergamot oil that causes phototoxicity. Bergapten-free bergamot essential oil or synthetics are now used in perfumery.