Our brains can give rise to all manner of odd psychiatric problems, but one of the strangest is trichotillomania better known as hair-pulling. The uncontrollable desire to yank out one’s hair may seem like a freaky sideshow diagnosis, but the disorder is actually not so uncommon, affecting perhaps two million American adults over 22. Exact numbers are hard to come by, since people with the condition often hide it sometimes they don’t even appear in public because of their embarrassing, mangy bald spots.