Why do the male private parts shrink in cold weather?

Chris - There is actually a physiology behind this. It's not just people claiming this and making up. It is true, honest.

The reason for this is, in fact, the rate at which sperm is made in the testes occurs optimally at a temperature which is 1 degree below body temperature, so about 36 degrees where normal body temperature is 37 degrees C. That's why they dangle down in a little bag to keep them a little bit cooler than body temperature.

Sperm actually can be stored and live quite happily at a higher temperature, and so that's why, when a sperm has been made, it can survive inside the female genital tract. But the actual synthetic process occurs better at the lower temperature and that's why the testes are dangling down.

You have enveloping, or wrapping-around, the testes in the scrotum muscles called the cremaster muscles; there's a reflex called the "cremaster reflex", which shortens those muscles to bring the testes up closer to the body when they're cold and also when you're scared, for obvious reasons! Because terror can mean you have to run away, or you might get booted somewhere sensitive, so you can elevate them out of harm's way.

So, you can bring them up closer to the body when you are cold and you drop them down a bit when you are too hot to keep the temperature right for making sperm at the right rate.

That's why things tend to get closer to the body and therefore appear to shrink when it's cold, and they dangle down a bit further when it's a bit warmer. So there is some real sound science behind this!