Shrinkage: cold, stress and the gym

Why your cock and balls pull back in the pool, before a date or after a workout, and why none of it says anything about the size that counts

You step out of the pool, or off the treadmill, or into a room where someone you fancy is already undressed, and your cock has quietly packed its bags. The balls have gone with it, pulled up somewhere near the ribs. Every man knows the feeling, and a famous 1990s sitcom episode even gave it a name. Shrinkage is not a measurement of anything. It is a reflex, and a rather clever one.

Soft is not switched off

The first surprise is that a soft cock is not relaxed. The erectile tissue is a sponge of blood spaces lined with smooth muscle, and in the flaccid state that muscle is held in steady contraction, letting in only enough blood to keep the tissue fed. An erection happens when the muscle lets go and the spaces fill. Softness is the active state; hardness is the release.

That contraction is run mostly by the sympathetic nervous system, the same wiring that handles fight or flight. The urologists who described it put it plainly: the flaccid penis is in a moderate state of contraction, and you can tell because it shrinks even further in cold weather, or when doctors inject a drug that tightens smooth muscle. There is no single soft size, only a range the nervous system moves you along all day.

This is also why soft measurements are so slippery. When a team of andrology specialists measured 201 men for a study, they did it in a private room held at 21 °C. Nobody, as far as we could find, has published a study that measures the same men soft at different temperatures and reports how many centimetres go missing. The percentages you may see online, "cold water takes off 30%" and the like, come from blogs, not from data.

Cold water and the pool

Cold makes the body pull blood away from the skin and the extremities to protect the core, and the penis is very much an extremity. Add the extra smooth muscle tone described above and you get the classic post-swim look: shorter and narrower.

The scrotum does its own thing, with its own muscles. The dartos, a thin layer of smooth muscle in the scrotal skin, is controlled by the sympathetic nerves and tightens the sack. The cremaster lifts the testicles towards the body. Together they shrink and raise the whole package to keep the balls warm (the Scrotum chapter has the details). The skin of the scrotum normally sits at about 34 °C and most pools are a good deal colder, so the effect can be dramatic, and it reverses as you warm up.

Stress, nerves and adrenaline

Because the soft state is kept by the sympathetic system, anything that turns that system up makes things smaller. Adrenaline and noradrenaline tighten the smooth muscle in the erectile tissue. In animal studies, stimulating the sympathetic nerves or infusing adrenaline makes an erect penis go down, and men whose erection problems are psychological have been found to have higher noradrenaline levels in the blood.

In plain words: anxiety shrinks. A medical exam, a first date, the first minutes in a sauna where you do not know anyone yet. Your body has decided it may need to run, and running does not need a penis. It is also why nerves make it harder to get hard.

The gym and the run

Exercise is a sympathetic workout too. Heart rate goes up, blood is sent to the working muscles, and the genitals are low on the list. The clearest data concern the balls: in eleven long-distance runners running naked on a treadmill for an hour, the scrotum warmed up right after the start while the rest of the skin cooled. The authors' best explanation was that the dartos and cremaster had pulled the scrotum up against the body, driven by the rise in sympathetic activity.

For the penis itself we found no study measuring length before and after exercise. The mechanism makes shrinkage likely, the locker room confirms it, but the size of the effect is unknown.

Nicotine

Nicotine tightens blood vessels, and it reaches the penis. In a controlled trial, 28 young non-smoking men chewed either a nicotine gum, about the dose of one strong cigarette, or a placebo, and then watched erotic films. With nicotine their erectile response was 23% smaller, and it was smaller in 16 of the 20 men with usable recordings, although they did not feel any less aroused. It measured erections, not the soft state, but it shows how fast one dose reaches the plumbing.

Why it means nothing for the real size

Soft size was already a poor preview of erect size before you got cold. In a classic study of 80 men, neither soft length nor age predicted erect length well. Shrinkage adds noise to a number that was saying little anyway. The cock that looks tiny after a cold shower is the same cock it was an hour ago, and when hard it will be exactly the size it always is. Growers know this better than anyone: Grower or shower? has the full story.

The worry, though, is real. In an Italian clinic, 67 men asked for surgery to lengthen a penis they felt was too short. None of them was below the 2.5th percentile of the normal range, and two in three said they were unhappy only with how it looked soft. That is the locker room talking. In gay spaces the locker room is not even a metaphor: gyms, saunas and pool showers are where men look at each other, and where everybody is at his coldest and most self-conscious.