Gymnophobia is a fear of nudity, whether it’s that person or someone else’s naked body. This fear might come alive most in dreams, but sometimes it might spill over into waking life.
A cultural example is Tobias Funke (played by David Cross) from “Arrested Development,” who was shown to be a “never nude:” He had serious problems stripping down, even for a shower. (The term has unofficially become the slang definition for the condition over a decade later. Seriously, ask your friends if they know what gymnophobia is, and then what a never nude is.)
But what percentage of the population are actually gymnophobes/never-nudes?
Unfortunately, there’s not any hard (heh) data on it. My guess is that since most sex-related data is self-reported (short of measuring blood flow to the genitals), people aren’t going to come forward to admit that they have this phobia. It makes logical sense, but hardly satisfies my curiosity.