You settle down on the toilet and get ready to get down to business. But suddenly, you’re met with a distraction: Your nose starts running. You don’t have a cold, and your schnoz was suspiciously snot-free when you headed into the bathroom, so why is it running overtime now?

If you often find yourself blowing your nose while you’re on the can, you might have thought it was just a coincidence. But it’s actually more common than you think—so much so that it actually has a fancy name to describe what’s going on.

It’s called defecation rhinorrhea, and, you guessed it, it basically just means a runny nose when you’re pooping (Can an orgasm really clear your congestion? We explore).

To understand why this happens, you need to understand what your body is doing when you poop in the first place.

"The bowels are regulated by a complex coordination of nerve signals," says Michael Rice, M.D., gastroenterologist at the University of Michigan's Michigan Medicine Gastroenterology Clinic.

Your gastrointestinal (GI) tract is controlled by your autonomic nervous system, which is made up of the sympathetic and parasympathetic nerves that coordinate with each other to keep your body functioning without any conscious effort—this includes functions like regulating your heart rate, blood pressure, temperature, sexual response, tears, digestion... and defecation.

Basically, the parasympathetic nerve fibers in your pelvis are responsible for triggering the peristaltic contractions in your lower colon, which move waste through your digestive tract and eventually evacuate your stool, Dr. Rice says (Here's why coffee makes you poop).

Those same autonomic nerves that are triggered to help you push your poop along also regulate the blood supply to your nasal area and the secretion of mucus, he says. So when your body is prepping to poop, it also fires up nerves in your nasal regions as a byproduct, too—which can cause the blood vessels in your nose to widen.

Basically, pooping puts your body in sensory overdrive, dilating the vessels in your nasal region, resulting in the runny nose.

It’s all a connection with your defecation process—it doesn't really have as much to do with your pooping posture as you may think. Still, it is possible that leaning forward while you poop may allow for previously released nasal secretions to trickle down your nose, rather than down the back of your throat, as they would if you were leaning back or lying down, Dr. Rice says.

So leaning forward can make a runny nose appear worse, and it’s also not doing your pooping goal any favors, either. A better posture is to sit properly—back straight and upright—with both feet on a thick phone book or a low level step for more of a squatted position, says Christine Lee, M.D., gastroenterologist at the Cleveland Clinic. This puts your rectum at a better angle, which makes it easier to poop (That's one reason why devices like the help you poop).

Related: 5 things you must try when you just can't poop).

It’s also possible that your runny nose while pooping is caused by something called vasomotor rhinitis, in which an irritant to the nose—think strong odors, humidity, temperature change, or even an emotional change—triggers the mucus production and release.

Still, "although emotions and particularly pungent odors (when you go to the bathroom) may lead to rhinorrhea, it is unlikely to be the primary mechanism behind defecation rhinorrhea," Dr. Rice says.

Bottom line is, your runny nose while pooping is a normal physiological response. It’s usually nothing to be worried about if it only occurs when you’re trying to poop, he says.

Save Your Own Ass!:

If your runny nose is persistent or associated with headaches, fever, dizziness or events such as head/nose trauma, you should see your doctor, says Dr. Rice.

In a really rare case, if you’ve recently had a head injury or brain or sinus injury or surgery, it could signal something called a cerebrospinal fluid (CSF) leak, where the fluid that surrounds the brain is leaking via the skull through the nose, says Dr. Lee. In that case, you’d likely notice that leaning forward and bearing down worsens the runny nose.

Emily Shiffer Emily Shiffer is a former digital web producer for Men’s Health and Prevention, and is currently a freelancer writer specializing in health, weight loss, and fitness.

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