Fetishes are much on the minds of some people, and there is money to be made from them (them being the fetishes and the people). This study zooms in on one part of the picture:
“Fetishistic Preferences of Clients as Ranked by a Sex Worker,” Zack Zdenek Cernovsky [pictured here], Journal of Sex and Marital Therapy, epub July 2015. (Thanks to Neuroskeptic and Ivan Oransky for bringing this to our attention.) The author, at Western University in Ontario,
A former escort girl and stripper, now a retired lady in her 40s, of intelligence at the level comparable to university graduates, was interviewed about unusual sexual requests of her former clients. She reported that most frequent requests were (1) those involving a foot or shoe fetish, (2) those to sell to the male client her underwear, and (3) those to urinate into her underwear before selling it to the client.
For a more encompassing view, read about the great attempt to catalog all fetishes (including the pacemaker fetish).
For some of the peripheral — yet medically important — constraints, see the study “An Industrial Hygienist Looks at Porn.”