It’s no secret that your dick has a mind of its own.

Sometimes it cooperates. Sometimes it lets you down. And sometimes (probably every day), it’s the first thing you notice when you wake up with a raging boner—otherwise known as “morning wood.”

Throughout the ages, philosophers, doctors, psychoanalysts, psychiatrists, and sexologists have studied sleep-related erections. However, it wasn’t until 1920 that Austrian psychoanalyst Wilhelm Stekel acknowledged that morning wood was a naturally occurring phenomenon in healthy men of all ages with healthy erectile function.

But why exactly do you wake up with wood? And more importantly, what does morning wood say about your overall health?

What Is Morning Wood?

Morning wood is the slang term for nocturnal penile tumescence (NPT). As sophisticated as that sounds, it’s simple: you wake up with an erect penis.

The earliest recorded history of morning wood dates back to the 15th century when ecclesiastical juries would observe men accused of having erectile dysfunction while they slept to see if they got erections in their sleep. If he couldn’t, his wife was allowed to divorce him.

That’s enough history for today. So, why does your penis wake up before you do?

What Causes Morning Wood?

Until recently, morning wood has been a mysterious phenomenon. However, physicians have few scientific explanations for why you start each day with a salute to the sun.

REM Sleep

As you enter the rapid eye movement (REM) phase of sleep, your brain starts to shut off some neurotransmitters. One of these is norepinephrine, which essentially ensures that you don’t walk around with a boner all day.

In more scientific terms, norepinephrine restricts the blood vessels in your penis. However, when you’re in a deep sleep, those blood vessels open up, leading to an erection. 

Testosterone Production

Your body pumps out hormones when you sleep, one of which is testosterone. This is the primary male sex hormone responsible for your body hair, deep voice, and of course, erections.

Your testosterone secretion reaches its peak just after you wake up, which correlates with morning erections. The testosterone level theory also explains why morning wood becomes less frequent with age.

Less testosterone, less wood.

A Full Bladder

As your bladder bloats with pee throughout the night, it stimulates a region of your spinal cord that can trigger a “reflex erection.” This is your body’s way to prevent you from wetting the bed. Ironically, trying to pee with a boner is one of the most difficult male maneuvers out there.

A common misconception about morning wood is that it means you’re horny. This might be true in some cases. But most of the time, your morning stiffy has nothing to do with sexual arousal.

One survey found that most men aren’t even aroused when they wake up with an erection. They felt their penis was ‘“in the way’” more than anything else.

How Often Should You Get Morning Wood?

According to Adam Ramin, M.D., director of Urology Cancer Specialists in Los Angeles, you should expect to get three to five nighttime erections. A healthy man will usually spend about 25% of the night with an erection—that’s about one every 90 minutes.

Not sure if you get nocturnal erections? Try the postage stamp test.

Place a few connected postage stamps on your flaccid penis before you go to sleep. If the perforated connections are broken when you wake up, you have evidence of a bedtime boner.

But what if the stamps don’t split?

Is It Normal to Have a Lack of Morning Wood?

If you’re consistently not waking up with your willy standing tall, it may be a health issue and you might want to seek professional medical advice. Don't hesitate to ask your healthcare provider what’s going on. It could be a sign of erectile dysfunction, nerve malfunction, arterial disease, hypertension, diabetes, and low testosterone.

“Consistently having erections while you sleep indicates healthy blood flow to your penis, which also is necessary for getting hard when you’re turned on,” says Tobias Köhler MD, an associate professor and residency program director of the urology division at Southern Illinois University’s School of Medicine. “If you experience erection problems when you’re trying to get busy — but you get them overnight or when you wake up in the morning — that points more to a psychological cause of erectile dysfunction, like performance anxiety or depression.”

Morning wood may not be convenient, but it’s one of the most reliable signs of sexual health. Think of that as the silver lining as you contort your body to take a leak tomorrow morning.