Nocturnal emissions are most common during teenage and early adult years. However, nocturnal emissions may happen any time after puberty. They may be accompanied by erotic dreams, and the emission may happen without erection. Dreams, if recalled at all, may not be erotic, or they may be confusing to the dreamer, especially if he is an adolescent, immediately after his first wet dream. The sensations, if any, which accompany a wet dream may range anywhere from simply a tingling sensation to a sense of urinating or having to urinate, instead of the typical orgasm (which is why many teens might awaken in embarrassment believing they have just wet the bed). It is possible to wake up during, or to simply sleep through, the ejaculation in what is sometimes called a "sex dream". Women can also experience orgasms in their sleep.
Nocturnal emissions occur as a physical response to erotic dreams and as a mechanism to expel an abundance of sperm cells, which are constantly in production within the male individual.
In the 18th and 19th century, if a patient had spontaneous orgasms frequently or released more semen than is typical, then he was diagnosed with a disease called spermatorrhoea or seminal weakness. A variety of drugs and other treatments, including circumcision and castration, were advised to treat this "disease". Some modern doctors, especially herb healers, continue to diagnose and advise treatments for cases of spermatorrhoea, but these treatments have not been validated by thorough experimentation.
Two passages in the Bible teach that under the law of Moses a man who had a nocturnal emission incurred ritual defilement.
The regulations required the defiled person (mtumma) to bathe in a mikveh. A man who had normal intercourse with his wife was also considered ceremonially unclean, and he too was required to bathe in a mikveh and he became pure after the sun had set (Leviticus 15:18). Leviticus makes similar statements about menstruation (15:19-24) and childbirth (Leviticus 12). Psalms are still recited on Yom Kippur at night as a supposed aid against nocturnal emissions. This is particularly an issue on Yom Kippur, since bathing is forbidden that day.
It is also possible that some of the above is referring to not a discharge of semen but of blood or other substance indicating disease. In fact the Bible lists two different types of emission, one requiring a wait only until the nightfall (nocturnal emission, or intercourse), but the other lasting a week (both requiring bathing in a mikveh). The second type of discharge is a non-normal one (for example pus), indicative of disease. Even the phrase "nocturnal emission" may be a mistranslation of a more dangerous type of emission.
Saint Augustine interprets the references to the uncleanliness of discharge of seed (and menstruation) in Leviticus as symbolising disorder and unruliness as opposed to the seed forming a human being through conception which symbolises the form and structure of a just life.