For many, the ringing of the alarm clock in the morning can be an unpleasant sound to wake up to. Accompanied by this unpleasant sound is the highly inconvenient phenomenon grown men, little boys, and even males in utero all experience: nocturnal penile tumescence (NPT), also known as “morning wood.” Unlike the Bermuda Triangle, this is not one of life’s unresolved mysteries, and ASAP Science's “The Science of 'Morning Wood” pulls back the covers on how and why morning erections occur.  

The physiological reaction that affects half the world’s population happens when males are sound asleep. NPT, just like clitoral erections, has been associated with rapid eye movement (REM) sleep. During this stage, the brain begins to shut off some neurotransmitters in an effort to regulate the body and stop you from acting out your dreams. Norepinephrine, a neurotransmitter that happens to be involved with the control of erections, causes vasoconstriction of penis blood vessels, which actually prevent an erection.

“It's like a stop sign to blood flow, but as you enter REM sleep, norepinephrine decreases and testosterone-related actions are now able to take place. This leads to vasodilation, or increased blood flow to the blood vessels, ultimately causing an erection,” says ASAP Science. During the sleep cycle, the extra blood increases oxygenation as it serves as a system of repair and helps to maintain functionality. Morning wood is just a remnant of REM sleep, which is why men wake up to erections.

“Morning glory” should not be solely regarded as an inconvenience; it supposedly can provide men with the psychological benefit of preventing urination during sleep. Urine retention during the night can cause the bladder to become full and cause the penis to be engorged and often erect, says ASAP Science. According to this theory, the penis stands erect in the morning to prompt men to wake up and use the bathroom. However, this may sound plausible since the body does have other methods to prevent men from wetting the bed, and can actually make it difficult for men to pee in the morning.

Overall, morning erections are secondary to the timing of REM sleep and the physiological processes associated with this stage of sleep for men. In fact, morning wood is completely normal — a lack of it may actually suggest a problem related to erectile dysfunction. A study published in The Urologic Clinics of North America noted NPT monitoring remains the best single non-invasive examination to distinguish between organic from psychogenic impotence.

Men, be happy you can pitch a tent without any camping skills whatsoever.