Shivering is an involuntary response to coldness. This tightening and relaxing of muscles in quick succession causes a slight bodily shake or tremble. It’s your body’s way of generating heat.

This momentary cold sensation or cold jolt can rip through your body unexpectedly — sometimes starting in the spine and moving downward.

But shivering doesn’t only occur when you’re cold. It can also happen when scared or excited. And if you’re like some people, you may experience something known as “pee shivers,” either after urinating or during the release of urine.

This weird phenomenon is unofficially called post-micturition convulsion syndrome. Oddly enough, there doesn’t appear to be a concrete explanation for why this occurs, but there are a couple of theories.

Shivering while peeing can happen to anyone, and can occur as young as infancy. Maybe you’ve seen a baby shiver for no apparent reason before needing a diaper change.

This can be a comical — or alarming — sight, depending on the extent of the shake. In all likelihood, however, what you witnessed was a harmless pee shiver.

Even though urination chills can happen to anyone, some may experience shivering more than others. Anecdotally, it happens to more males than females. But there aren’t any studies to support this.

Despite the lack of research on this topic, one theory is that a change in body temperature in the groin area triggers pee shivers in some people.

When you remove your undergarments to urinate, this exposes previously warm private parts to a lower room temperature or cold air.

This can make you feel colder, and as a result, your body might shiver to bring warmth back to your body.

Another plausible explanation is that the release of warm urine from your body causes a slight decrease in your body temperature. In this case, your body may respond instinctively with a shiver to generate heat and warm up.

Pee shivers may also have something to do with your central nervous system (CNS), or more specifically, mixed signals in your nervous system.

This makes sense, given how the central nervous system controls the bladder.

The peripheral nervous system sends information from the brain and spinal cord to other parts of the body. This part of the nervous system also includes the autonomic nervous system (ANS), which regulates involuntary bodily functions.

According to Caleb Backe, a health and wellness expert for Maple Holistics, your autonomic nervous system plays a vital role in the process of urination.

The ANS is divided into two parts. The sympathetic system is the emergency system that regulates your fight-of-flight reflex. The parasympathetic system relaxes the body and returns it to a resting state.

“When your bladder gets full, it activates nerves in the spinal cord known as the sacral nerves. This brings the parasympathetic nervous system into action, causing your bladder wall to prepare to push urine out of the body,” says Backe. “When urine leaves the body, blood pressure drops, prompting a [reactive response] from the sympathetic nervous system.”

The sympathetic nervous system then floods the body with neurotransmitters called catecholamines in an effort to restore blood pressure.

This creates a mixed signal between the two nervous system components, which may in turn trigger an involuntary pee shiver, notes Backe.

As a side point, blood pressure tends to elevate when standing. Since men commonly urinate standing up, it’s possible that they experience a more significant drop in blood pressure during urination. This might explain why men have pee shivers more than women.

The bottom line is that no one knows for certain why pee shivers happen.

Yes, there’s sound reason to back up a few explanations. But many of the original theories on this condition date back to a 1994 online discussion board conversation, which has no medical significance.

The term coined for this occurrence, “post-micturition convulsion syndrome,” is not a condition doctors recognize, and there are no controlled, scientific studies on the topic.

Of course, this doesn’t change the fact that pee shivers are real and happen to many people. For now, though, we have to rely on educated guesses with regard to “why.”

Researchers may provide a more concrete explanation for these occurrences in the future.

Pee shivers might be due to a sudden drop in body temperature, or mixed signals in your nervous system. They are harmless.

This doesn’t mean you should ignore all unusual occurrences that happen during urination. See a doctor if you experience fainting, dizziness, or burning while urinating, or if you have blood in your urine.