"Generally speaking, a wet dream occurs when we experience sexual arousal during sleep. This is especially common in men, since we naturally experience erections during the REM (rapid eye movement) phase of sleep. Combine that with an erotic dream, and there’s a good chance you’ll wake up in a (wet) spot of bother. There’s also some utility to wet dreams: “For men, nocturnal emissions are a way for the body to clear out old sperm,” Ley explains. “Sperm has an expiration date, and if you haven’t ejaculated in a while, your body gets rid of the old stuff to ensure the sperm on tap is fresh and ready to hit the field of play.”"