Morning wood — or as it’s formally known, nocturnal penile tumescence (NPT) — is a common occurrence for many people. From time to time, you may wake up with an erect penis. This is most common in younger men, although men of all ages may experience NPT.

Many people assume a morning erection is a sign of sexual stimulation. However, this is not always the case. Morning wood is likely the response your body has to one of several natural occurrences.

We use “boys” and “men” in this article to reflect the terms that have been historically used to gender people. But your gender identity may not align with how your body responds to this occurrence.

The cause of NPT is likely dependent on many factors. Doctors have a few theories that help explain why people wake up with an erect penis from time to time, but none of these theories are supported by concrete, medical evidence.

These theories include:

Physical stimulation

Though your eyes are shut, your body is still aware of what’s happening around you. If you or your partner accidentally touch or graze your genitals, you may become erect. Your body senses the stimulation and responds with an erection.

Hormone shifts

Your testosterone level is at its highest in the morning after you wake up. It is highest immediately after waking up from the rapid eye movement (REM) sleep stage.

The increase in this hormone alone may be enough to cause an erection, even in the absence of any physical stimulation.

As men get older, usually between ages 40 and 50, natural testosterone levels begin to fall. As this level decreases, episodes of NPT may decrease as well.

Brain relaxation

During your waking hours, your body releases hormones to suppress erections. When you’re asleep, your body releases less of those hormones. Combine this with other reasons you may experience an erection in your sleep, and NPT becomes more likely.

What’s clearer is what does not cause morning wood. For example, needing to urinate is not responsible for morning wood. Some people believe a morning erection keeps them from urinating during their sleep, but this is not true.

Morning wood is not always a sign of sexual stimulation. In many cases, NPT is not caused by dreams or thoughts of a sexual nature.

Men of all ages can experience NPT. It’s healthy at any age and is a sign of a properly functioning blood and nervous system in and around the penis.

Boys may experience NPT as young as infancy. NPT may also occur in men in their 60s and 70s. It will become less frequent as erectile dysfunction (ED) issues begin to occur, and those issues become more frequent with age.

You may experience an erection three to five times each night. Unrelated to what’s in your dreams, NPT can last longer than 30 minutes. Some men may experience an erection for as long as 2 hours during their sleep. Most erections will ease within a few minutes of waking up.

Having an erect penis when you wake is an indicator of healthy blood and nerve supply to the penis. The presence of NPT also likely indicates that you’re physically capable of getting and maintaining an erection while awake.

If you stop experiencing NPT or notice that you’re not waking up with an erect penis anymore, this may be an early sign of an underlying medical problem.

Most likely, this is a sign of physical ED. You may have something happening within your body that’s preventing adequate blood or nerve supply for proper erectile function. You may be more likely to experience ED if you:

People with certain disabilities may also be more likely to experience ED.

Medications may affect your ability to experience morning wood. Painkillers and some antidepressant medications may prevent NPT.

NPT may become less common as you get older, but if you’re young and are not experiencing a morning erection or if your erections suddenly stop, it may be time to contact a doctor.

Morning wood is healthy, and it’s rarely a reason to contact your doctor. However, two situations may mean it’s time to make an appointment. These include:

You stop having morning wood

If you frequently experienced morning wood but now are not experiencing it at all or have fewer erections, you should talk with a doctor.

While it’s natural for episodes of NPT to occur less frequently with age, a sudden drop in frequency may be a sign of an underlying medical problem.

You begin experiencing painful erections

Most morning erections will subside within 30 minutes of waking up. If your erections last more than an hour after you wake up or if they become painful, you should make an appointment with a doctor.

It’s hard to declare “too much” and “too little” when it comes to NPT. Some people experience a morning erection every day. Some experience it less than once a week.

During your annual physical exam, talk with your doctor about how frequently you’re experiencing morning wood. If you’re not experiencing it enough, your doctor may be able to help diagnose a reason.

Morning wood is very common. It’s an indication of typical blood and nerve supply to the penis. Most young men will experience morning wood several times per week. As men grow older, they begin experiencing it less frequently.

If you stop experiencing NPT, this may be an early sign of an underlying medical problem. Pay attention to how often you experience morning wood. If it stops, speak with a doctor.