Causes the victim's skin to break out in boils.
- George Weasley: "Half our year had minor breakdowns coming up to OWLs. Tears and tantrums… Patricia Stimpson kept coming over faint…"
- Fred Weasley: "Kenneth Towler came out in boils, d'you remember?"
- George Weasley: "That's 'cause you put Bulbadox powder in his pyjamas"
- Fred Weasley: "Oh, yeah, I'd forgotten… hard to keep track sometimes, isn't it?"
- — Fred and George talking about their O.W.L. year[src]
- Harry Potter and the Order of the Phoenix (Mentioned only)