Andrew Siegel, MD
** This is equally relevant for the ladies as well as the gentlemen! Women get sleep erections just as men do, although obviously not as dramatic. Don’t forget that the clitoris is the female counterpart to the penis and it is qualitatively the same, although smaller in stature.
There are 3 reasons humans experience erections: psychogenic, reflex, and nocturnal (sleep). Psychogenic erections are caused by erotic thoughts or sensual stimulation through vision, hearing or smell. Reflex erections occur in response to touch—sensory nerve impulses travel from the genitals to the spinal cord centers and then from the spinal cord centers back to the genitals. Nocturnal erections have a unique mechanism controlled by the brainstem.
Erections of the male penis and female clitoris can and do happen in non-sexual circumstances, particularly during sleep. Sleep erections often occur during a phase of sleep known as rapid eye movement (REM) sleep. During a typical night of sleep, 4-5 episodes of REM sleep will occur, each lasting about 10-15 minutes, at which time both dreams and erections are prominent. Interestingly, the content of dreams at the time of sleep-related erections is rarely erotic in nature. Of note, female REM sleep related clitoral erections occur along with other signs of arousal including vaginal lubrication.
Sleep erections are most prominent during puberty and gradually lessen with aging. As we get older, episodes of sleep erections become come fewer, shorter, less intense and begin later in the sleep cycle.
There seems to be a relationship between quality of sleeping and dreaming and the presence of sleep erections. Those who have the best quality sleep and dreams seem to have the best quality sleep erections, followed by poor sleepers/good dreamers, followed by good sleepers/poor dreamers and followed by poor sleepers/poor dreamers.
Q. Why do we get sleep erections?
A. The purpose behind sleep related erections is theorized to be to improve the oxygenation of the smooth muscle of the erectile tissue of the penis and clitoris to help maintain normal erections.
In the non-erect state, the blood oxygenation in the erectile tissue is 20–40 mm, while in the erect state it is 90–100 mm. It is thought that the flaccid state with its low oxygenation favors collagen and connective tissue formation in the smooth muscle of the erectile chambers, resulting in scarring and the potential for problems in achieving erections.
The hormone testosterone and the ED medications Viagra, Levitra, Cialis and Stendra have been found to improve the frequency, magnitude, duration and rigidity of sleep erections.
Bottom line: Sleep erections, present in both sexes, are a mechanism for protecting the anatomy and function of the erectile tissues, another clever trick that nature has devised to help ensure reproduction.
Reference: van Driel MF: Sleep-Related Erections Throughout the Ages. J Sex Med 2014;11:1867-1875