Although the risk of hypothermia in Canada — with its frigid temperatures and frozen rivers and lakes — may seem obvious, it's possible to experience the deadly effects of the cold just about anywhere.

This includes exercising outdoors in chilly weather or spending too much time in relatively mild water.

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)

Humans don't have a layer of fur or blubber to keep them warm so we need clothes to maintain our body temperature at around 37 C. That's the temperature at which our body is designed to function at its optimum.

As you start to cool, though, your body sends warning signals. You will feel cold if body temperature falls to 36 C, and at 35 C, you will start shivering as your body tries desperately to generate heat.

Stepping out of the cold is often enough to help get your internal temperature back up, but ignoring the signs could lead to a further drop in body 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 be in danger of collapsing. At that point, you should be taken to the nearest hospital.

If your temperature falls to 27 C, you will likely be unconscious and could die.

Who's at risk

The very young are often more at risk than adults to developing hypothermia: they lose heat more quickly than adults. 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 — people with a condition like Alzheimer's may not fully realize the danger of going outside in the winter 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 winter 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 to drink them, 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.

Hypothermic 'miracle'

There have been some amazing recoveries from hypothermia.

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 made a recovery.

In February 2001, 13-month-old Erika Nordby of Edmonton crawled outside the family home in the middle of the night. The 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.