Sexuality Stack Exchange Archive

Is Nocturnal penile tumescence aka “morning wood” result of sexual arousal?

Most, if not all, men are familiar with this: many times we wake up with an erection, phenomenon known as Nocturnal penile tumescence, or in more common wording, morning wood.

Most of what I read describe it as being a way for the body to prevent urine leaking during sleep.

While erection by itself is something sexual, I still wonder if this specific case of erection might be purely a bodily function not related to sexuality, same way for example that urinating isn’t something sexual even though it involves sex organ.

So my question is, are there any studies about it claiming one way or the other?

Answer 216

Stop-urine-hypothesis is a myth

I think the stop-urine-leaking-story is a myth. I never heard of this idea before, and read it here for the first time in my life. I think this is completely nonsense. It would mean, that you would pee in your bed if your body wouldn't produce the erection. But I'm sure you remember days where you woke up with a limp penis and the urgent need to go to toilet immediately, but without having leaked into your bed.

But it is true, that you find a lot of resources written in english that discuss this possibility (I'm a German native speaker. I never found serious resources written in German mentioning this idea).

Up to 5 erections each night

Lets have a look at the medical term “nocturnal penile tumescence”:

“nocturnal” = nightly
Nightly (nocturnal) means “during the night”. It does NOT mean “in the morning” or “when waking up”

“penile” = has to do with the penis

“tumescence” = swelling
(mainly in the sense of normal engorgement of the penis or the clitoris)

So: “nocturnal penile tumescence” = “nightly</strong> penis swelling”</p> </blockquote>

Fact is, that the penis erects during sleep not only a few minutes before we awake. It gets hard (and falls down again in the unerected state) multiple times during the night, and this has nothing to do with sexual arousal. Even babies get between 1 to 5 erections during a normal night. Also very old men, who can no longer get an erection by sexual stimulation while awake can get those nightly erections (without noticing it because they are sleeping). And each of those erections can last between 15 and 40 minutes (sometimes even longer).

Only when you suffer from an erectile dysfunction, you can't get nightly erections. And a very simple test on erectile dysfunction uses this fact: Stick some stamps around your penis when going to sleep. The nightly erections will tear apart the stamps, which proofs, that you can get erections. If the stamps aren't torn apart, the chance is high that you have a medical problem that makes it impossible to get an erection.

For the test on erectile dysfunction see https://en.wikipedia.org/wiki/Tumescence section “Nocturnal penile tumescence testing”, item 2.

The reason is dreaming

The simple reason for the nightly erections is: dreaming. When you have a dream, not only your eyes are moving fast (REM = rapid eye movement). Also your heart is beating faster and the frequency of breath increases. But still your body lays there very comfortable and relaxed--the best conditions for the blood to flow into the penis and build up an erection.

It doesn't matter what you are dreaming of. A dream with sexual content doesn't produce a harder or longer erection than any other dream. Only when the dream is a nightmare, where you have strong negative emotions, are you unlikely to get an erection, because your body is not as relaxed during a nightmare as during a normal dream.

see also: Cycle of Penile Erection Synchronous With Dreaming (REM) Sleep (scientific paper)

“Wet” dreams

When you didn't ejaculate for a longer period of time, it can happen that during one of those dreams even semen is emitted, but without having an orgasm. (This depends on how you define “male orgasm”. When you say male orgasm = emission of semen, then you have an orgasm per definition, otherwise not.) When you wake up and see what happened, many people think it was because of a sexual dream (which in fact is very likely), but it can also happen while dreaming of something very different. So a “wet” dream (“nocturnal emission” in doctor-speach) often really is a sexual dream, but not always.

See also this article in Young Men's Health about nocturnal emissions (“wet” dreams)

“Morning wood” = last nightly erection

The longer you are sleeping, the more likely it is that you are dreaming (see: Timing of REM-sleep in Wikipedia). You don't dream really much during the fist few hours of sleeping, but in the hours before you wake up, you have more dreams. And so, this is also the time where you have more erections.

When you wake up during a dream, or short after a dream, it is very likely that you wake up while having one of those nightly erections, so the “morning wood” is just the last nightly erection of a night.

btw: When talking about dreams, you should know that your brain erases memories on dreams very quickly. So many people can't remember their dreams. Many even don't remember that they did dream at all, but the fact is that every person is dreaming every night. If you really don't dream you a have very serious medical problems.

Men only?

Also interesting to know:
Under the same situations where sleeping men get an erection, a woman will get a wet vagina, the clitoris will rise and the labia will bulge. So women wake up with the symptoms of sexual arousal as often as men, but since there in fact is no real arousal, and since those anatomic changes are not so visible on women as an men, the female counterpart of male “morning wood” is widely unknown.

Resources

In addition to the resources linked above, here are also some resources in German language (my native language).

## Answer 170 - posted by: [nus](https://stackexchange.com/users/151634/nus) on 2015-07-30 - score: 3

There is two distinct things that might have an influence on this phenomenon:

  1. Most importantly, the heart beat rate during sleep is on average, at least according to one study 8% slower than awake. When waking up the acceleration of your heart beat as well as hormonal releases will cause your blood pressure to go up. This is the most likely reason you wake up with an erection.
  2. Men have higher testosterone levels in the morning, which might mean extra sexual arousal in the morning.
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