Men with thinning hair might as well finish the job, suggests a recent paper in Social Psychological and Science. Albert Mannes, who studies at Wharton—and who, full disclosure, is happily bald—found that women judged the same man differently depending on how much hair was on his head. Blame action heroes and athletes, perhaps, but bald outperformed partially bald on every measure. Facial hair also can shape the way a woman sees a potential mate, reports a study in Evolution and Human Behavior. Men with thick stubble were rated the most attractive, while those sporting full beards were seen as the most fatherly. Not sure what to do with that razor, or why Mr. Clean makes you weak-kneed? A shave and a haircut are not always best—here's a cheat sheet.