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12 Things That Happen to Your Body When It’s Freezing Out

When the temperature drops below freezing, the human body uses these incredible mechanisms to try to stay warm.

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There’s a reason why you hate being cold

As any outdoor enthusiast will tell you, “cold kills.” Your body temperature only has to drop about three to four degrees Fahrenheit for you to slip into hypothermia. At that point, you’ll start to shiver and begin to struggle with decision-making, according to Montana health officials, where extreme cold is top of mind.

So, how does cold weather affect your body? Here’s what can happen.

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Your blood vessels constrict

Your body is built to always maintain a stable core temperature of 98.6 degrees Fahrenheit (37 degrees Celsius). When the temperature in your environment drops to freezing cold, thermoreceptors in your skin sound the alarm, alerting an area of the brain called the hypothalamus, which acts like a thermostat dedicated to maintaining that 98.6-degree equilibrium, according to Robert Kenefick, PhD, research physiologist at the U.S. Army Research Institute of Environmental Medicine. One of the first actions the hypothalamus takes: It tightens the blood vessels in your arms, hands, feet, and legs. “Blood delivers heat to the skin,” says Gordon Giesbrecht, PhD, professor of thermophysiology at the University of Manitoba in Canada. “If you decrease blood flow to the skin, you decrease heat loss from the skin.”

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You have to urinate

All that vasoconstriction forces fluid to concentrate in your core, says Kenefick. This causes volume receptors that talk to your hypothalamus to say, “Hey, maybe you should get rid of some of that fluid—maybe you should pee.” It’s common, say, on the ski slopes for people to use the bathroom right before they head outdoors and then to feel like they need to go again shortly after being outside. (Check out these surprising health benefits of cold weather.)

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You shiver

Of course you shiver when it’s cold—but the reason you do is interesting. “When vasoconstriction isn’t doing enough to warm you, the hypothalamus tells your muscles to start contracting,” says Giesbrecht. “One of the byproducts of muscle contraction is heat.” Garden-variety shivering produces about 100 watts of heat, he says. If you get cold enough to enter into mild hypothermia, you can produce 400 to 600 watts of heat through shivering.

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You freeze much faster if wet

Why do little kids still shiver when they get out of a heated swimming pool in 80-degree weather? “Water carries heat away from the body 25 times faster than air, so you can lose a great amount of heat very quickly when you’re wet,” says Kenefick. “Shivering is one way your body is trying to raise your core temperature back up.”

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You make things worse if you drink alcohol

Think a flask filled with the strong stuff can keep you toasty? You might be dead wrong. The body’s first major reaction to cold is to constrict blood vessels, but  “alcohol does the opposite—it causes peripheral vasodilation,” explains Kenefick. “Those blood vessels widen and dump all this heat to the environment.” Your skin will feel warm, but that provides a false sense of security, because this really causes your core temperature to drop, which can lead in extreme cases to hypothermia

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You can become too cold if you dress too warmly

How’s this scenario for ironic? You’re outside in very cold weather shoveling snow, which is a lot of physical work. You’re contracting muscles and generating a lot of heat, so your core temperature actually goes up. “In this situation, your blood vessels dilate instead of constrict, and you start sweating. If that sweat then gets trapped in your clothing, then it can start sucking heat away from your body. That’s a recipe for hypothermia right there,” says Kenefick. The lesson: Don’t overdress if you know you’re going to be exercising vigorously.

(Love the cold? Check out these perfect winter wonderland vacations.)

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You scrunch down and huddle with others

When your body has constricted your blood vessels and made your muscles start shivering, you might also instinctually engage in social behaviours that help conserve heat, says Kenefick. When you scrunch down and make yourself smaller, you lose less heat to the environment because you decrease your own surface area.

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Over time, your brain stops operating on all cylinders

Once your body goes into a hypothermic state—a core temperature that’s too low—your brain and nervous system have a harder time functioning and maintaining normal thought. “The hypothalamus tries all the mechanisms that usually work—and then when those fail, it becomes unclear of what to do next,” Kenefick says. “People have been found in freezing cold temperatures with all their clothes off, because the hypothalamus said, ‘OK, well, let’s try dumping heat out there—making people feel hot—and see if that will work.”

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Your skin turns white and hard

These are signs of frostbite, a condition when your exposed skin gets too cold and freezes. Cheeks, nose, and fingers tend to be especially vulnerable because they are getting less blood flow because of the vasoconstriction. Also, your fingers are cylinders, which gives them more surface area relative to their size and makes them more vulnerable to heat loss. Frostbite means the skin tissue has become damaged. If it’s severe enough, says Kenefick, it can turn black and actually fall off. At first you will feel pain; as your skin gets colder and colder, it will feel numb. “When this happens, the thermoreceptors in your skin have stopped working,” Giesbrecht says.

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Your skin gets rashy and red

Some people have an allergic reaction to cold—but not necessarily freezing—weather, a condition known as cold urticaria or less formally, “winter bumps.” It’s not a reaction to freezing cold weather, like frostbite, but rather just dry, cool conditions, which can cause an allergic-type reaction in certain people with sensitive skin. (Here’s what everyone gets wrong about winter skincare.)

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You have trouble catching your breath

Normally when you inhale air, your nose helps moisten, humidify, and warm it before it moves down to the lungs. But in some people, like patients with asthma, or in some cases where the weather is just so bitter cold, the air doesn’t warm up enough first, which causes the lungs to spasm and constrict, which makes breathing difficult, says Kenefick.

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Your muscles go on the fritz

As muscle tissue cools, it doesn’t work as well, says Giesbrecht. “At first, you lose the ability to do fine motor tasks, like using your cell phone correctly,” he says. “Then eventually (as your bigger muscle groups are affected), you might not, say, be able to hold on to an overturned boat in cold waters.”

Next, learn how the cold weather can actually enhance signs of aging.