In a post about the science of sleep twitching, a reader brought up an unknown (to me) phenomenon: Pee shivers. Apparently these are experienced by a relatively large portion of the male population, and today we shall take a look at why.
By popular request . . . this is for you.
Sadly, this astonishing mystery has never been extensively studied. It's a sudden shudder, usually at the end of urination. It happens most often to males, but in rare cases, females experience it as well. Like the mighty myoclonus (the twitch), doctors have advanced far enough in understanding to give this reaction a long name: post-micturition convulsion syndrome. (This is where we play science detective. Not many of you know this, but 'post' often means 'after'. Or it means 'an oblong block of wood set into the ground.' In this case I believe it's most likely to mean 'after.' 'Convulsion' is a synonym for 'shudder' or 'shiver.' The dictionary taught me that. 'Syndrome' is a group of symptoms that occur in certain people; and so it explains that some people chronically have some difficulties, while others never do. And from the context, I would guess that 'micturition' means 'peeing.') So by examining its name we have found that that is it called, basically, 'after-peeing-shiver-thing-that-happens-to-certain-people.'
As to why it happens; no one really knows. There are two major schools of thought. One insists it's just a reflex to a drop in temperature. While peeing, certain parts are exposed which would otherwise be covered (I would hope). This causes a drop in body temperature. Urination also involves letting a lot of warm liquid out of the body, and so losing a lot of heat. This also causes a drop in body temperature. And even if the bathroom the pee-er is in isn't cold, the parts of the body that are exposed are accustomed to being bundled up in clothes that keep them at a higher temperature, so any exposure to the air would seem cold to those parts and make the body shudder to warm them.
The other main school of thought is this is a quirk of the autonomic nervous system. This is a pretty safe guess, since the autonomic nervous system is in control of many involuntary bodily functions. Anything you do without thinking about, like closing your eyes when you sneeze, is the result of the ANS taking charge. Some of the stuff that it does, though, has to be handed over to the conscious mind eventually. When we are going about our daily lives in public, the ANS keeps the bladder relaxed and all the various valves between the bladder and the outside world tensed. It does so without us thinking about it, which is good, because if it didn't, our response to every question would be, "Look, I'm just trying to concentrate on not peeing on you," and our society would not have advanced very far.
When we actually urinate, we voluntarily relax the valves and tense the bladder, sweeping aside the unconscious process we've been keeping up for most of our lives. Since that unconscious process involves fairly hardcore brain chemicals like dopamine and epinephrine, and the since the more we have to hold in, the more of those chemicals the brain has to put out to make sure we don't have an accident, the sudden switchover could invoke a twitching response in the body.
Or it could be that ghosts are watching you and laughing. Enjoy your next trip to the bathroom.