Some science behind the scenes
Furanocoumarins, or furocoumarins, are produced by a variety of plants. The chemical structure of furanocoumarins consists of a ‘furan ring’ fused with coumarin [see coumarin].
Many [not all] furanocoumarins are toxic and are produced by plants as a defense mechanism against various types of predators ranging from insects to mammals. It responsible for the dermatitis some people get when exposed to wild parsnip and the Giant Hogweed.