Alex Snigurowicz shows the frostbite on his toes at a hospital in Anchorage, Alaska, on May 28, 2005. Snigurowicz and two climbing partners had been rescued at the 5,000-metre level of Mount Logan, Canada's highest mountain. (Al Grillo/Associated Press)

Once the wind chill makes the temperature feel like –28 or colder, exposed skin can freeze in under 30 minutes. When it drops to –40, frostbite can occur in less than 10 minutes. Take it to –55, and you're in danger within two minutes. Anything colder than that and Environment Canada warns you shouldn't go outside at all.

Your body doesn't appreciate being exposed to the cold for too long, so it takes protective action. It puts most of its energy into keeping your core — where your internal organs are located — as warm as possible. Unfortunately, your toes, fingers, cheeks and ears may pay a steep price for keeping the rest of your body toasty.

How do I know if I have frostbite?

You might not, in some cases.

But normally, the first sign of frostbite is a stinging or burning sensation in skin that has been exposed to the cold for too long. The length of time depends on how cold it is — or how bad the wind chill.

Exposed skin will become red and swollen before the stinging or burning sensation kicks in. If it remains exposed, the skin will feel like it is tingling and it will turn white and waxy as the frostbite progresses.

These sensations occur because less blood is flowing to the body's extremities. With a loss of warming blood flow, the fluid within your cells and tissues start to freeze, forming ice crystals and causing physical damage and permanent changes in cell chemistry.

Skin could become blistered or turn black if not treated promptly.

How is frostbite treated?

You have to warm up your body. Carefully.

It's best to get the afflicted person to a hospital emergency room. If that's not possible, find shelter and give first aid as quickly as possible.

Thaw the affected area by:

• Immersing the frostbitten area in warm water (no more than 40 C).
• Drying and covering the area with warm clothes followed by layers of blankets.
• Holding frostbitten fingers close to warm parts of the body, such as under the armpits.

The patient should also drink hot fluids to help warm the body and increase blood flow to the extremities.

Do not:

• Drink alcohol or smoke.
• Rub, apply snow to, or put intense, direct heat on the frostbitten areas.
• Walk on frozen feet or toes.

Rewarming the frostbitten area can take up to an hour and can cause pain as the skin thaws. If the frostbite is not severe, the skin should return to its normal colour and feeling should also return to normal. If there is pain, you can take acetaminophen, ibuprofen, or aspirin.

Tissue injury is greatest when cooling is slow, cold exposure is prolonged, the rate of rewarming is slow, and, especially, when tissue is partially thawed and refreezes.

If the frostbitten areas do not look normal after thawing, you should get to a hospital as soon as possible.

How do I protect myself from frostbite?

Stay out of extreme cold. If you must go out, dress appropriately — layers of clothing work best.

If you are out longer than expected, or weather conditions deteriorate, seek shelter.

Other steps you can take include:

• Make sure your clothing protects your head, ears, nose, hands, and feet. Also, try to keep your hands and feet dry.
• Watch for any numbness or prickly feelings, which may mean that you are starting to get frostbitten.
• Avoid alcoholic beverages, which might cause you to ignore signs of frostbite.
• Keep your hands warm by tucking them in your armpits periodically.
• Be aware of wind chill values.

How long do the effects of frostbite last?

It depends on how bad the frostbite is. In mild cases, the problems can go away once the skin is rewarmed.

In severe cases, the effects can last for weeks. Frostbitten skin could be sensitive to the cold for several months.

When blood vessels beneath the skin are damaged by frostbite, the blood supply can be cut off, killing the tissue. Dead tissue can become infected, leading to gangrene. In severe cases, gangrene can lead to amputation of limbs or — if the infection is severe — death.

What else should I worry about in extreme cold?

You could get frostnip — sort of like frostbite-lite. Frostnip occurs when ice crystals form under the skin. If you are aware of it early enough and take action, you may be able to avoid getting frostbite. However, frostbite can occur within a couple of minutes of frostnip.

Chilblains occur when bare skin is exposed to cold water, or when wet skin cools. The skin itches and swells. This can be caused by wearing damp boots. Chilblains can lead to gangrene.

Mountain frostbite is a variation observed among mountain climbers and others exposed to extremely cold temperatures at high altitude. It combines tissue freezing with hypoxia — a shortage of oxygen in the body — and general body dehydration.

Hypothermia results when body temperature falls below 35 C. Symptoms include drowsiness, impaired co-ordination and weakness. It can also be fatal.