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Why Is Four Hours the Magic Number for Having an Erection for Too Long?

Almost universally, doctors say priapism — an erection that lasts longer than four hours — is an ER-worthy condition. But what happens around the fourth hour that makes it any different from the third?

There’s one specific joke associated with the idea of a prolonged erection, and it goes: “If I had an erection that lasted for hours, I’d call everybody I know, not the doctor!” It’s a line repeated by L.A.-based urologist Dudley Danoff when we speak — but, as he assures me, long-lasting erections are, in fact, no joke.

The medical name for an erection that you can’t get rid of is priapism, and, according to the NHS U.K., it happens when the blood that fills the penis to make it erect gets trapped and can’t flow back out again. If this happens and isn’t treated immediately, it can cause long-term impotence. Or as Danoff more eloquently explains: “The sausage casing that holds the blood has got a very intricate kind of mechanism, and if the blood stays in there and sludges, then the structure of the corpora cavernosa, or the spongy tissue in the shaft of your penis, becomes fibrotic, and that causes impotence.”

Danoff says that priapism — which isn’t related to arousal — is a “fairly uncommon occurrence,” but explains that it’s often caused when someone self-injects a “vasoactive substance” into their penis — aka something to make it erect, or to induce longer-lasting erections as a treatment for erectile dysfunction. It can also be caused by excessive use of PDE 5 inhibitors like Viagra, or, as Danoff calls it, “overdoing the weekend warrior bit.” In some cases, priapism can happen as a side effect of conditions that affect the blood, for example sickle cell disease or leukemia.

Doctors famously say that if you’ve been suffering with this plight for four hours, you need to seek immediate medical attention — but, the question remains, why four hours specifically? 

“I’m not sure,” Danoff answers. “I guess it’s arbitrary. I would assume that over the years, urologists have decided that if the erection lasts less than, say, three hours, it’s not problematic, but over four hours, it potentially is and needs medical attention.” 

According to WebMD, the four-hour cut-off has to do with how long it takes to cut off the supply of fresh blood to the penis. Simply, it takes around four hours for the blood in the penis to be deprived of oxygen — and that can cause serious damage.

If it’s been less than four hours, though, NHS U.K. suggests that you do gentle exercise, take a warm bath or try and pee to eradicate your erection. You can also take paracetamol or ibuprofen to relieve some discomfort. But if it’s been more than four hours, it’s off to the emergency room for you, where a doctor will, according to Danoff, “drain [your penis] with a big needle to try and remove the sludge.” “It really is a true urological emergency,” he concludes. 

So, if you ever find yourself with a four hour erection, don’t jokingly call your friends — call the doctor!