When it comes to science, some things are investigated a little bit more enthusiastically than others. It makes sense, of course — trying to cure diseases and solve problems that affect millions naturally takes priority over less pressing scientific questions like “Why do some people’s ass cracks go really high up?”
And so, unsurprisingly, one field that hasn’t had a lot of investigation is shuddering while pissing. Not everyone experiences it, but it’s a common enough occurrence for many — mid-or post-stream, a shiver runs down one’s back as though the body is clamoring to add a bit of jazz to proceedings. It’s sometimes accompanied by a kind of “Hud-d-d-d-d-d” noise from the mouth, the type of sound a cold horse would make.
To date, all the thinking behind it is purely speculative, based on anecdotal evidence and light-hearted online surveys (see above for why). The more legitimate-sounding name given to the phenomenon, “post-micturition convulsion syndrome,” wasn’t coined by a scientist or doctor but an IT consultant on a forum associated with the long-running Chicago Reader column “The Straight Dope.”
Some people claim to experience it more when drunk, peeing in a public bathroom or just doing particularly hefty pees. There are theories that it’s caused by heat loss as warm urine exits the body, but if that were the case, vomiting or taking a big dump would also cause shudders (which might even occasionally come in handy in the latter case if it’s just, you know, hanging there).
The prevailing theory, however, is that it’s caused by a collision of signals rushing between the brain and the pee-hole, coming from the two divisions of the autonomic nervous system.
The sympathetic nervous system, the majority of the time, works to maintain homeostasis and keep everything as regular as possible. It regulates things like heart rate and blood pressure, unconscious processes that the body just gets on with without you having to actively engage them, and reacts swiftly when conditions change. It also controls what muscles are unconsciously relaxed and contracted — without it doing this, pee would just dribble out of you all the time unless you constantly, consciously, contracted your urethral muscles. Life would be both smelly and exhausting.
The parasympathetic nervous system looks after things like digestion, salivating, tear production, sexual arousal and excretion. Most of these processes take place unconsciously, but some parts — the exact whens of peeing and pooping — are controlled more consciously. When you pee, the parasympathetic nervous system causes your adrenal glands to release certain hormones known as catecholamines — epinephrine, norepinephrine and dopamine — to prompt an increase in blood pressure, which, in turn, prompts the internal urethra and bladder neck to relax and the external sphincter muscles to open.
Urine leaving the body then causes an immediate drop in blood pressure. Regulation of blood pressure is a key function of the sympathetic nervous system, and these two pressure shifts in rapid succession create a mixed signal that results in an involuntary shudder. Think of it as a momentary glitch.
The blood pressure drop is more pronounced if (a) standing, hence men tending to experience it more; and (b) doing a particularly large piss. This might explain people feeling like they experience it more when drinking. The dopamine involved can also lead to mild brief euphoria, hence the occasional moan of pleasure emanating from the middle of a big cloud of piss steam.
Until the world of science solves a reasonably long list of more important problems, this sensible-sounding theory will have to do. The good news is, it’s nothing to worry about, just a quirk of the human body. However, there are conditions adjacent to it that can be legitimate causes for concern. Micturition syncope is a loss of consciousness after a piss, which is risky for all the reasons you’d expect sudden bathroom-based unconsciousness to be. Post-micturition syndrome, which is caused by an over-distended bladder, can be connected with bladder paraganglioma, a rare but serious condition involving tumors growing in the bladder. Post-micturition dribble (also known as the apocalyptic-sounding “post-void dribble”) can be an early symptom of urethral diverticulum or prostatitis.
But a simple bit of piss-shiver is just a sprinkling of fun on an otherwise mundane activity, some shuddery icing on a urinal cake.