Maybe you came across the Dec. 17, 2008 issue of the British Medical Journal and read the article that debunked the myth that  you lose more heat through your head than from any other part of your body. Maybe that got you thinking, "I don't need to wear that hat mom's always trying to make me wear."

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Ph.D. student Andreas Flouris (left) and Dr. Stephen Cheung monitor the water temperature as Constance Tweedie, a fourth-year kinesiology student, sits in a tub of ice cold water at Dalhousie University in Halifax, as part of research into hypothermia. ((Ryan Taplin/Canadian Press))

Well, it's always good to heed mom's advice — she knows how best to keep you warm. And it's not just because she cares. Let your body get too cold and you're at increased risk for hypothermia.

Humans don't have a layer of fur or blubber to keep them warm like other warm-blooded animals. We need clothes — and when it's especially cold outside, we need more layers to maintain our body temperature at around 37 C. That's the temperature at which our body is designed to function at its optimum.

If you don't protect yourself with appropriate clothing, your body won't be able to generate as much heat as it's losing to the really cold air around you.

If your body temperature falls below 35 C, you will become hypothermic and will need medical attention of some kind.

But your body sends warning signals before you reach that point. You will feel cold if your body temperature falls to 36 C. At 35 C, you will start shivering as your body tries desperately to generate heat.

Stepping out of the cold — or out of the wind — is often enough to help get your internal temperature back up, but ignoring the signs could lead to a further drop in your body's temperature.

At 34 C, you may seem clumsy, irrational or confused. At 33 C, you will experience muscle stiffness. By the time your body temperature hits 32 C, you will stop shivering and you're in danger of collapsing. You should be taken to the nearest hospital.

If your temperature falls to 28 C, you will likely be unconscious and you may suffer cardiac arrest.

Hypothermic 'miracle'

On Dec. 19, 2008, 55-year-old Donna Molnar of Ancaster, Ont., left home in a snowstorm to pick up groceries. She was found three days later, in a field unable to move, under 60 centimetres of snow, slowly freezing.

Her body temperature had fallen to 30 C. However, she did not suffer organ damage and is continuing to recover.

In February 2001, 13-month-old Erika Nordby of Edmonton crawled outside the family home in the middle of the night. The outside temperature was -24 C. By time she was found, her body temperature had tumbled to 16 C and her heart had stopped.

It took a team of more than a dozen medical staff an hour and a half to get her heart beating again.

Three days later, Erika was suffering from severe frostbite, but there were no signs of major physical injury or the brain damage that's expected in someone whose oxygen supply to the brain has been cut off, especially for that amount of time.

Such recoveries from extreme hypothermia are extremely rare. Doctors believe Erika entered a type of hibernation that allowed her to survive.

More often, extreme cases of exposure to cold end tragically, like that of seven-year-old James Delorey. He wandered from his home in South Bar, near Sydney, Nova Scotia on Dec. 5, 2009 wearing jeans, a shirt and a vest — nothing to protect him from the cold and snow that would hit the area later that day. He was found unconscious in thick bush two days later, just over a kilometre from his home.

Delorey was airlifted to hospital in Halifax, but did not survive the night.

Who's at risk

The very young are often more at risk than adults to developing hypothermia: they lose heat more quickly than adults do. If you're over the age of 65, you may also be at greater risk of developing hypothermia as advanced age, illnesses and medications may make you more susceptible to it.

Other risk factors include mental impairment — if you have a condition like Alzheimer's, you may not fully realize the danger you could be facing by going outside in the winter when you're not properly dressed.

Alcohol and drug use may also increase your risk. You might feel warm all over after a couple of stiff drinks, but alcohol lowers your body's ability to retain heat. It also impairs your judgment.

But hypothermia is not just a cold weather phenomenon. Get stuck in a downpour on a cool day and you run the risk of developing hypothermia if you don't get inside and get out of those wet clothes.

If you like exercising outdoors, you need to take precautions in cooler — but not cold — temperatures. Go for a long, hard bike ride — or run a marathon — when the temperature falls below 10 C, and you may be at risk. You'll feel warm as your body works hard, but once you stop, you will cool off quickly — especially if you are sweating and the wind is blowing.

As your body cools, it will draw heat from your extremities in order to keep your core warm. Your hands or feet may begin to look very pale as your body cools.

You can also develop hypothermia by spending time in cold water. If you fall into an icy river or stream in the middle of winter, you will develop hypothermia in less than 15 minutes. You likely won't survive if you're in the water for 45 minutes.

If you've gone south, however, and fallen off a deep-sea fishing boat in the Gulf of Mexico during the winter months, the relatively mild water temperatures will keep hypothermia at bay for a couple of hours.

What to do

If you're with someone who may have hypothermia, you should get them medical help as soon as possible — especially if that person is shivering, appears disoriented, shows a lack of co-ordination, has cold and pale skin, appears tired, and is slurring speech. Try to get the person indoors where you can keep them warm and dry until help arrives.

Other things you can do include:

  • Remove wet clothing and replace it with a dry covering.
  • Insulate the person from the ground with a blanket.
  • Use your body heat to help warm up the person. 
  • If the person is able, provide warm non-alcoholic beverages.

You should not apply direct heat to the person through a heating pad, hot water or a heating lamp. You can apply warm compresses to the chest, neck and groin areas. Do not massage or rub the person. People with hypothermia are at increased risk of cardiac arrest and should be handled gently.