Why...in cold water, do nipples go erect, but willies shrink?

Answer 1

Nipples become erect in the cold as nature's way of assisting a baby during the breastfeeding process. As soon as a woman take her boob out of her shirt, the cooler air causes the nipple to become erect, thereby allowing an infant to begin feeding.

A guy's dick shrinks from the exposure to cold water as a means of self protection against what the body perceives as a hostile environment. Besides his dick shrinking and drawing closer to his body, a guy's scrotum will tighten and draw his balls closer to his body...again as a means of self protection against damaging his reproductive capabilities.

Both are examples of nature's attempt at the preservation of our species.

Hope this helps.

Answer 2

Your penis size varies depending on how much blood is flowing through it. In general, when you are cold, your body will shunt blood away from the peripheral parts of your body and keep it all in the interior of your body. That means you will have less blood flow in your skin...and less blood flow in your penis. The point is to save heat. If you have a lot of blood flowing into the peripheral parts of your body, you will lose heat there.

Your nipples work by a different mechanism. They become erect because of the contraction of smooth muscle underneath the areolar skin. (This next part is me hypothesizing based on what I know about human anatomy and physiology in general) In the cold, the smooth muscles contract in order to reduce the skin's surface area to minimize heat loss and help keep the milk ducts underneath the skin from being potentially damaged by the cold. The nipple becomes "erect" for two reasons. There is extra tissue right under the nipple, so when the areola contracts, that little bit of extra tissue will make the nipple naturally protrude. There are also more bits of smooth muscle under the nipple and around the milk ducts that lead lead to the nipple. These tighten up the tissue underneath the nipple--making it hard.

You'll see a similar behavior with the skin of the scrotum--albeit a much more developed response (it has more muscle under the skin) since temperature control there is much more important. When it's cold, muscles underneath the skin contract making the scrotum shrink. This keeps the testes warm by moving them closer to the body and minimizing heat loss through the skin.