Finally, might some astronauts have masturbated? Not only is it possible, it’s probable as at least one mission physician recommended it to the astronauts out of concern for infected prostate glands. I’m not making this up. The Apollo 11 command module pilot Michael Collins, writing in his book Liftoff, states about the Skylab mission:
“One doctor advised regular masturbation, advice [Skylab crew member] Joe [Kerwin] ignored.” Later, he writes: “There was no sex on Skylab.” And still later, he addresses the possibility of recreation in space: “And lovemaking! I don’t think any astronauts have yet been privileged to sample the ultimate use of weightlessness.”
Note that he only states that one of the astronauts ignored the advice on masturbation, not all of them. Hmmm.
http://blog.chron.com/sciguy/2007/02/has-it-been-done-in-space-before/