Sexual fetishes run the gamut, from drinking blood to dressing up like cute animals to wearing diapers. What causes fetishes? There's no clear answer. "Why would a man develop a mask fetish?" asks Dr. Barry McCarthy, a therapist in Washington, D.C. "Could be something he read as a kid that's tied to 16th century Spain, who knows." Whatever is causing the fetish, he says, it takes control of the individual's sexuality.