Methoxsalen is a drug used to treat psoriasis, eczema, vitiligo, and some cutaneous lymphomas in conjunction with exposing the skin to UVA light from lamps or sunlight. Methoxsalen modifies the way skin cells receive the UVA radiation, allegedly clearing up the disease. Levels of individual patient PUVA exposure were originally determined using the Fitzpatrick scale. The scale was developed after patients demonstrated symptoms of phototoxicity after oral ingestion of Methoxsalen followed by PUVA therapy. Chemically, methoxsalen belongs to a class of organic natural molecules known as furanocoumarins. They consist of coumarin annulated with furan. It can also be injected and used topically.

n 1970, Nielsen extracted 8-methoxypsoralen from four species of the genus Heracleum in the carrot family Apiaceae, including Heracleum mantegazzianum and Heracleum sphondylium. An additional 32 species of the genus Heracleum were found to contain 5-methoxypsoralen (bergapten) or other furanocoumarins.

Author John Howard Griffin (1920–1980) used the chemical to darken his skin in order to investigate racial segregation in the American South. He wrote the book Black Like Me (1961) about his experiences.

Formal Chemical Name (IUPAC)
9-methoxy-7H-furo[3,2-g]chromen-7-one

References

https://en.wikipedia.org/wiki/Methoxsalen