Here's Why You Get a Boner When You're Dead Asleep

by Elizabeth Millard, Marty Munson
·5 min read
Photo credit: ViewStock - Getty Images
Photo credit: ViewStock - Getty Images

You wake up from a deep sleep to notice that every part of you has been relaxed and resting except for one thing: your penis Middle-of-the-night erections—also known as morning wood, since you often notice them when you awake—are pretty damn common. In fact, they should be.

Regular nighttime erections can actually signal that your body is in good health, A healthy man can expect to get hard three to five times per night, each one lasting between 30 and 60 minutes, according to the University of California, San Francisco Medical Center.

Doctors call these erections while you sleep "nocturnal penile tumescence"—and they can serve as an indicator of how your entire body is functioning. They also are helpful when it comes to diagnosing the root of an individual’s erectile dysfunction. Sometimes, it’s challenging to determine if someone’s ED is physiological (due to something like diabetes or low testosterone) or psychological (due to anxiety, sexual trauma, etc.). If you’re able to get erect in the middle of the night with regularity, you know that your ED is being caused by something psychological and not physiological.

To learn all about nighttime erections, we spoke to Adam Ramin, M.D., urologist and medical director of Urology Cancer Specialists in Los Angeles. He was able to explain how nighttime erections work, why we get them, and what it means if you’re not having erections while you’ll sleep.

Understanding sleep erections means understanding how erections work in the first place.

To understand more about nighttime erections and morning wood, we need to first understand how erections work in general, Ramin says. Stimulation in your parasympathetic nervous system—say, when you see something sexy or feel a touch—causes the release of neurotransmitters.

That leads to the dilation of the arteries in the penis. As a result, more blood flows into the penis, less blood flows out, and your erection grows and gets hard.

Photo credit: Men's Health
Photo credit: Men's Health

During sleep, there’s a general increase in the activity of that same parasympathetic system. This is what slows your heart rate, relaxes your muscles, and kicks off a deeper dream state. It’s also what sparks the development of nocturnal erections.

So nighttime erections aren't a result of touching your penis inadvertently or having sexy dreams. They're all about your nervous system, Ramin emphasizes.

Why do people get nighttime erections?

But that still leaves open the question: What's the point of this automatic response? Nobody really knows.

“There is no true purpose to development of nocturnal erections,” he says. “They are merely a byproduct of a natural stimulation of the parasympathetic nervous system at night.”

So even though scientists aren't sure why they exist, sleeping boners can end up helping your erection in the long run, urologist Tobias Köhler, M.D., M.P.H., told Men’s Health previously. These erections keep your penile tissue soft and stretchy. They also prompt the smooth muscles in your penis to relax, allowing the blood to rush in and get you hard. That keeps it in fighting shape for when you’re awake and need it.

Without this regular sleepytime workout, the muscles may become too contracted, and eventually, the length of your erect penis may shorten, Köhler says.

What if I don't get nighttime erections?

Although it’s often tough to determine if you’re getting the proper amount of nighttime erections, you should either notice them if you awaken at night, or wake up at full mast sometimes.

If you never do—or if you don’t notice it as frequently—you might want to mention it to your doctor, Ramin advises. Some medical problems could be at play like nerve malfunction, arterial disease, hypertension, or diabetes. It’s also possible you may have low testosterone since men whose levels fall below average tend to pop fewer erections at night, according to researchers from the University of California.

Even depression or anxiety could lead to parasympathetic nerve malfunction, affecting both your daytime and nighttime boners. If you notice a change in your nighttime erections, best thing to do is get it checked out. And try these lifestyle tips for how to get stronger erections and stay hard.

What if I'm not sure whether I'm having erections in my sleep?

Alright, let’s say you’re having erection issues during sex and you’re having trouble determining if you’re getting nighttime erections for the obvious reason that you’re asleep. The old test to see if you’re getting an erection while sleeping involved putting a roll of stamps on your penis and seeing if they’re broken when you wake up in the morning. (That would indicate that you had an erection.) This test isn’t full-proof, especially if you’re a restless sleeper who moves around a bunch.

If putting stamps on your peen isn't appealing—and we don't blame you—you can purchase a RigiScan, a portable home device to evaluate the quality of your nocturnal penile erections. Throughout the night, the machine repeatedly measures how much blood is in your penis and how well it can resist bending or buckling (giving a sense of how “hard” you are). The results are stored on the machine, making them simple to then share with your doctor.

Additional reporting provided by Michelle Malia.

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