psoralen
(SOR-uh-len)
A substance from plants that is sensitive to light (or can be activated by light). Psoralens are used together with UV light to treat psoriasis, vitiligo, and skin nodules of cutaneous T-cell lymphoma. They are also being studied in the treatment of graft-versus-host disease. Psoralen is a type of furocoumarin. An example of a psoralen is methoxsalen.