Windchill

Weather forecasters use an index to try to indicate how the average person will feel in the wind, this is known as wind chill.

The skin is our largest organ and is vital in temperature control. When we are hot we sweat, this removes excess heat and cools us down.

When we are cold, the skin warms a thin insulating boundary of air, trapping in body heat and keeping us warm.

There are 2 ways in which wind cools the skin, firstly it disturbs the insulating boundary layer of air, and secondly it increases the evaporation of moisture from the skin - this takes body warmth with it.

When the wind chill is below -50°C on an exposed forehead unconsciousness can occur in minutes, also skin may freeze within 30 seconds when the wind chill is -75°C.

Individual differences

The effects of wind chill affect people differently. Wind chill is based on the average person; however there are a number of factors that can cause differences in how we feel in a cold wind.

Extreme cold can cause both frost bite and hypothermia. Depending on your build, you can be more susceptible to one than the other.

If you are tall and thin you will probably feel cold sooner than shorter stockier people because you have a greater surface area of skin compared to their mass. People with greater insulation are more likely to suffer frost bite but less likely to suffer hypothermia, as they lose body heat to their cooling skin more slowly.

Young and elderly people have less developed and less effective body temperature control systems, so they are at particular risk from the cold. In Canada, where wind chill effects are very important, they have a 'Cold Weather Policy' where children are kept indoors when wind chill reaches a certain level.

If you have damaged blood vessels, which carry heat around the body, you are also more likely to feel the cold. This can be the case if your iron levels are low which can happen when taking some medications.

Metabolism rates can also have an impact on how cold you feel, as slow metabolism can result in poorer circulation.

Some medical conditions, or even medications, can also have an effect on how we feel in a cold wind.

If you have diabetes and have peripheral neuropathy (a disorder of the nerves) you may find that you sweat more on your face and neck - from which we lose a large proportion of our body heat. If your blood glucose levels are high this can also damage the nerves in your legs and feet, which means that cold may not be felt as easily - this makes you more likely to suffer frostbite when it is very cold.

If you take Beta-Blockers they can also increase the likelihood of frost-bite because they cause blood vessels to constrict, and this results in colder hands and feet.

Avoid the chill

Apart from staying inside on windy days, there are simple things that you can do to lessen the effects of wind chill.

Drink plenty of water to hydrate your skin inside and outside (dehydration affects your ability to regulate your body temperature) and if you apply moisturiser to wet skin this seals in the moisture and prevents heat loss.

When you go out in the cold make sure you wrap up well - wearing a hat and scarf can help keep in the 40 - 50% of heat that would otherwise be lost through the head and neck, mittens help keep hands warmer than gloves, and by wearing several thin layers of clothes you help create more insulating layers of boundary air.

Before going out if you eat a light snack rather than a big meal you will ensure that less blood goes to your stomach to aid digestion leaving more to circulate to the extremities of your body like fingers and toes.

If you wear waterproof clothes in wet weather they prevent the increase in heat loss from damp skin and clothes - heat loss occurs about 20 times faster from wet clothes than dry clothes.

When the wind is strong the body can react as if it is under attack - this creates the 'stress hormone' dopamine. The body can't sustain stress like this for long, which is why you may feel exhausted at the end of a windy day.