Some science behind the scenes

Furanocoumarin

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.