If you’re a man or if you’ve spent any time close to one, you’ve probably noticed the phenomenon of nocturnal penile tumescence — aka morning erections or, in slang, morning “wood.”
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
But why, exactly, does this happen? And is it ever a sign of a problem? Urologist Ryan Berglund, MD, answers your questions on the topic:
Q: Why exactly do morning erections occur?
A: The sacral nerve, part of your parasympathetic nervous system, controls erections.
The sympathetic nervous system is what prepares you for action — the fight or flight response. The parasympathetic nervous system, on the other hand, is what’s active while your body rests and repairs itself. It’s responsible for things like digestion, getting rid of waste, and sexual arousal.
The parasympathetic nervous system is active when you’re asleep, so erections sometimes happen in your sleep. The term “morning wood” is actually a misnomer; penises can become erect and then flaccid again several times in the course of one night. You’re just more likely to notice it when you wake up.
Q: There are a lot of explanations out there: dreams, a full bladder, REM sleep. Do any of these play a role?
A: Yes, but these really still link to the parasympathetic nervous system.
During REM sleep your parasympathetic nervous system is more active, and this is when you’re most likely to dream — and sometimes have an erotic dream, which can certainly result in an erection and maybe ejaculation.
A full bladder could press against and stimulate the sacral nerve.
Q: At what age is it normal for morning erections occur?
A: They can occur at any age — even male fetuses have erections in utero! It’s very common for friends of mine who are parents to call me up to ask if it’s a problem that their 3-year-old has an erection. The answer I always give them is that it’s totally normal.
Q: Can morning erections tell us anything about erectile dysfunction?
A: We know that erectile dysfunction is multifactorial — there are a lot of things that have an impact. Diminished neurological function, vascular issues, and anatomical or structural issues all sometimes cause erectile dysfunction.
On top of all these physical causes, there are sometimes psychological causes, too. It’s sometimes hard to determine what’s causing it.
What morning erections can tell us is whether the issue is physical or psychological.
I saw a patient today who told me that he developed erectile dysfunction recently, but he’s been under a tremendous amount of stress at work. In a case like this, morning erections would show that there’s probably nothing physically wrong and that the issue is psychological.
Issues in a relationship, trouble at work, or even sexual trauma can hamper erections. In those cases, eliminating the stress or conflict can solve the problem. Counseling with a therapist trained to treat erectile dysfunction can help.
Q: Should you ever worry about morning erections?
A: Priapism is a condition in which an erection lasts more than four hours. That can result in permanent dysfunction of the penis. Morning erections typically subside soon after you wake up. If you’re having erections that last significantly longer than that, it would be a good idea to speak to your doctor.
