It's phototoxic. If you touch it, getting the sap on you, and then expose that skin to sunlight, it causes blisters and scarring. That's caused by a chemical in

It's phototoxic. If you touch it, getting the sap on you, and then expose that skin to sunlight, it causes blisters and scarring. That's caused by a chemical in the plant called furanocoumarin. (If you touch it, wash that area with soap and cold water, and avoid exposing it to sunlight for at least 48 hours.) That's even mentioned in the lyrics to the Genesis song: "Strike by night! / They are defenceless / They all need the sun to photosensitize their venom"