Every Friday on the blog, I answer people’s questions about sex, love, and relationships. This week’s question comes from a reader who wanted to know why he wakes up with erections every morning.

Why do I always wake up with “morning wood?” Is it a sign that I dream about sex a lot?

Great question! Morning wood, known scientifically as “nocturnal penile tumescence,” is a completely natural occurrence for men at all stages of the life cycle (in fact, it even occurs in utero!). What happens is that, during the night, a series of neurological and hormonal changes occur as we cycle in and out of REM (rapid eye movement) sleep. These changes produce erections, independent of the content of our dreams. Certainly, sexy dreams may lead to arousal, but men will naturally experience 4-5 erections per night as a result of their sleep cycle no matter what they’re dreaming about. This means that guys don’t just have “morning” wood, they also have midnight wood, 4:00 AM wood, and so on.

Some scientists believe that these erections may actually serve an important biological purpose in that they can help maintain a healthy penis [1]. Specifically, by regularly bringing lots of oxygenated blood to the penis, it may promote tissue health, thereby staving off erectile dysfunction. So, when you look down and see morning wood, it’s kind of like your body telling you “system normal.”

On a side note, it’s a little known fact that women get “morning wood” too [2]. Yes, you read that right. It turns out that women get a similar number of clitoral erections during their sleep. This is probably not discussed as frequently because clitoral erections may not be as obvious and, unlike penile erections, they do not cause the same annoyance of impeding early morning urination.

For more on the science of morning wood, check out this fascinating video by ASAP Science.