Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Sometimes men wake up with an erection in the morning. Why does this happen?

share|improve this question
It is a little funny. One question about penis and 11 votes and ~900 views in 5 hours. LOL – WYSIWYG Jul 23 '14 at 15:44
It's because we all wonder - but he is the one who dared to ask. – Tomáš Zato Jul 23 '14 at 20:23
Relevant: – corsiKa Jul 24 '14 at 14:28
Haaag haaaaa...."Boner Wave"..That is an awesome concept! – I J Jul 25 '14 at 4:03
up vote 42 down vote accepted

Sometimes men wake up with an erection in the morning. Why does this happen?

Shortly speaking: REM (Rapid Eye Movement) is one phase of sleep. During this phase we dream and some of our neurotransmitter are shut off. This include norepinephrine, which is involved in controlling erection. Norepinephrine prevents blood to enter the penis (preventing the erection). In absence of norepinephrine (during REM phase norepinephrine is absent) blood enters the penis yielding to an erection. This phenomenon is called Nocturnal penile tumescence. Such erections typically occurs 3 to 5 times a night. A related question on the concern of women erections can be found here.

A high pressure in the bladder may also lead to a "reflex erection". This erection allows to prevent uncontrolled urination. The drawback is that when, in the morning one has an erection and can't wait to pee it might get hard to accurately target the toilets!

This video is also a nice and easy source of information on the subject.

Is it bad?

(Reading my "note" below, you have edited your post to get rid of this question, thank you)

It is perfectly healthy you don't have to worry about that. These erections are even thought as contributing to penile health. At the opposite, the absence of erections during the night are an index of Erectile Dysfunction (E.D.).


Be aware for future posts that medical questions are often considered as off-topic on this site. Asking "is it bad?" turns your question into a medical one. Health related questions (but not personal health) should be asked on health.SE

share|improve this answer
I just had to, had to signup to this site for the sake of upvoting this... man, this is crazy... – Awal Garg Jul 23 '14 at 11:45
How does the lack of norepinephrine affect women? – jnovacho Jul 23 '14 at 12:03
That sound's great... How do I permanently shutoff this norepinephrine?? :-D – Thihara Jul 23 '14 at 12:05
@Thihara Norepinephrine affects a lot more than just erections. Killing it from your system entirely would be a very bad idea. (Just FTR - I know, or at least really hope, your question was intended as sarcasm.) – Iszi Jul 23 '14 at 18:48
@jnovacho That sounds like a good question - you should ask it separately. – Iszi Jul 23 '14 at 18:49

protected by Chris Oct 19 '15 at 6:18

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.