The penis has three cylindrical bodies of tissue called the corpus cavernosum and corpus spongiosum that produce an erection when the tissues are filled with blood. These tissues are sponge like and consist of compartments that are interspersed with many blood vessels. When the blood vessels are dilated, the compartments fill with blood. The penis enlarges in length and width, becomes rigid and assumes a position that is elevated compared to its flaccid, soft or resting state. Thinking sexy thoughts produces nerve impulses from the brain that initiates the erection through a complicated series of nerve pathways.

Erections in adolescents may occur from lifting heavy loads and healthy adolescents usually have sleep related erections every night. Often these erections are associated with dreams or rapid eye movement (REM) sleep; teens may have as little as two erections or up to six erections each night. Sexual activity seems to have no significant effect on the number of nightly erections. It is usual for teen males to awaken with an erection in the morning. This is usually due to the stimulation of a full bladder. Some authors suggest that large amounts of seminal fluids may also cause erections in the sleeping or awakened adolescent.

Of course, the most common cause of erection in the adolescent male is sexual stimulation. According to Kinsey, a famous researcher of the human sexual response, a male’s first response to sexual stimulation is penile erection. Many adolescent males only need minimal sexual stimulation or sexual fantasy to achieve erection. After ejaculation, males lose their erection and there is a variable period of time before they can achieve another erection.

Erections that are prolonged due to disease may be painful. Termed priapism, this may be seen in males with sickle cell anemia. Males who cannot have erections may be impotent. Most teen males who cannot achieve erections do not have a disease process causing this problem. Rather, there may be a psychological barrier that is interfering with the capability to have an erection. Although it is unusual for male adolescents to require medication to achieve an erection, there may be circumstances where medication is indicated.

Virtually all males have experienced wet dreams or nocturnal emission. During puberty, sex hormones cause the testicles to produce sperm, and organs such as the prostate and seminal vesicles also produce other fluids that compose semen. Occasionally when these fluids build up in the body, a teen male will develop an erection during sleep followed by ejaculation or release of the semen. When this occurs during sleep, it is termed nocturnal emission. Some males may have romantic or sexy dreams when the emission occurs and others may not recall the dream. Although most males experience nocturnal emissions, some have them as frequently as a few times per week and some may have only one or two nocturnal emissions during their lifetime.

Nocturnal emissions will decrease or stop entirely when a male has ejaculation either through masturbation or sex with a partner.
Wet dreams are a normal and expected experience of adolescence. All young people are encouraged not to get worried when they get wet dreams in their slee.
It is all normal and health.