Why Cold Weather Makes You Pee

Increased Urination When You're Cold

You're more likely to need that outdoor toilet when it's cold outside than when it's warm.
As unpleasant as it may be, you're more likely to need that outdoor toilet when it's cold outside than when it's warm. Ulrich Mueller, Getty Images

Does it seem like you have to pee more when you're cold or when it's cold outside than when it's warm? It's not just your imagination! 

When you are cold, your body wants to protect your vital internal organs from the temperature change. It does this by constricting capillaries in your hands and feet through a process called peripheral vasoconstriction. Your extremities get cold, but toasty warm blood bathes your core.

This means there is more blood in a smaller volume, which raises blood pressure, causing your brain to signal the kidneys to remove liquid from your blood. Your urine volume is increased and you need to urinate.

In addition to the effects of vasoconstriction, cold temperatures change how permeable cells are to water. Proteins called aquaporins act as channels to allow water in and out of cells more quickly than through osmosis. When body temperature starts to drop, aquaporins limit the amount of water allowed into some cells, including kidney and brain cells. Less water going into cells translates into more water in the bloodstream. Here too, your brain tells your kidneys to remove the excess water, filling your bladder and making you need to pee.

If you drink an alcoholic beverage to feel warm, you'll likely make the situation even worse. The alcohol will dehydrate you, in part because it also inhibits aquaporins.

Alcohol acts as a diuretic, so your body thinks it needs even less water than it was holding onto before you took that first sip. Alcohol does make you feel warm but actually hastens hypothermia by expanding the capillaries. From this effect, you'd need to pee less, but the continued drop in temperature would eventually lead you to pee more and could kill you from cold.

Another factor to consider is perspiration. If you're cold, you're not losing moisture through perspiration. When it's hot, you're slowly (or quickly) becoming dehydrated by sweating. If you feel cold, you're retaining water compared with when you're warm.