>>2587859>>2587930So, here's why you really don't want to fuck with hogweed; the sap reacting with sunlight isn't technically what burns you. The sap contains a class of chemicals known as furanocoumarins. Furanocoumarins cause phytophotodermatitis in human skin; they strip the skin's ability to protect itself from UV. That protection doesn't come back when you remove the sap; the dermis has to completely regenerate itself first. So imagine washing a bunch of hogweed off yourself, thinking you're fine, then going back out into the light... only to find out a hour later you've got burns anyway.
Tl;Dr hogweed sucks, don't mess
