During puberty, a guy begins to produce semen in his testicles. Semen is the fluid that contains sperm, or reproductive cells, that can make a girl pregnant. It comes out of the tip of the penis when a guy ejaculates, or cums.

When teen guys first start producing semen, the testicles sometimes get overloaded and need to release some semen. Usually, that happens when a guy is sleeping. It�s called a wet dream. The technical name is �nocturnal emission.� It�s normal for boys to have a lot of wet dreams, anywhere from one to three times a week. It�s also normal for a guy to never have a wet dream or have only one his whole life. A guy who ejaculates on a regular basis, either during sex with someone or masturbating alone, is less likely to have wet dreams. They also tend to slow down as guys get older.