Bergapten psoriasis drug, molecular model. This drug is used to treat psoriasis, a chronic disease which causes red scaly patches to appear on the skin. These patches, or plaques, are inflamed areas of excessive skin cell production. Bergapten (like other drugs belonging to the furocoumarin family) is given orally or applied to the skin in the presence of ultraviolet A radiation, in a process known as phototherapy. This combination disrupts the overproduction of skin cells. Bergapten occurs naturally in some plants of the Apiaceae family, including celery and parsley. Atoms in this model are represented by coloured rods; carbon is blue, hydrogen is white and oxygen is green.