Heat and Cold

The human body has an optimum body temperature and therefore has developed mechanisms to maintain this when the environment changes. However, in spite of this, excessive heat or cold can cause injury and in extreme cases, serious or even fatal conditions. These conditions tend to be more marked in the very young and very old, whose temperature-regulation systems may be under-developed or impaired, respectively.

Maintenance of Temperature

Some methods of maintaining the body's temperature are passive, whilst others are active, most notably those that occur within the circulatory system and at the skin.

How the Body Keeps Warm

The body keeps warm by a number of actions. First there is the conversion of food into energy and muscle actions—voluntary (exercise) or involuntary (shivering). Heat can also be absorbed from external sources, such as the sun or a heat from a fire. In conditions of extreme cold the body constricts the blood vessels in the skin, so the body becomes pale, reduces sweating and erects body hairs to trap warm air at the skin.

How the Body Loses Heat

Heat may be lost to cool surrounding air from the skin, or from the breath, and by the placement of cool objects next to the skin, such as ice, which provides a pathway for heat to escape. The blood vessels in the skin dilate and the skin becomes flushed. Sweat glands may becomes active and heat is lost as the sweat escapes into the cooler air. The rate and depth of breathing increases, with warm air being expelled and cool air drawn in to replace it, cooling the blood.

Effects of Extreme Cold

The body reacts to cold by shutting down blood vessels in the skin to prevent 'core' temperature escaping. Deprived of warm blood, parts such as fingers or toes may, in extreme conditions, actually freeze, causing injury (frostbite). If the core temperature becomes dangerous low, bodily functions slow down (hypothermia) and may stop altogether.


Chilblains are hot, red, swollen patches of intensely itchy skin on the toes, feet, fingers and are caused by the exposure to cold and moisture. They usually disappear within a few days, although they can become chronic with dull violet discoloration of the skin and the appearance of painful blisters containing blood-stained fluid. Prevention is easier than cure, the condition hardly ever occurs in people with enough warm dry clothing in the colder seasons. The most effective treatment is the application of numbweed before covering the blisters with a light dressing if necessary.


This typically occurs in freezing and often dry and windy conditions. Casualties who cannot move are particularly vulnerable. The tissues of the extremities freeze, causing damage which may be superficial or deep. Minor cases ('frostnip') recover well, but severe frostbite can result in permanent damage. There may at first be 'pins-and-needles' with affected parts becoming pale. The parts will eventually become numb with the skin feeling hard and stiff. They will then turn white, then mottled and blue, and eventually black. Black discoloration is a result of a component of blood breaking down and in these circumstances, amputation may be necessary.

First check for other injuries such as broken bones, treating these with priority. Once treated, or if none, get the casualty to shelter, concentrating next on getting the patient warm and keeping them warm. Do -not- thaw frostbitten parts until shelter is reached. Very gently remove gloves and rings, or boots. You can then warm the part gently with your hands, or in your lap or alternatively in the casualty's armpit.

Do -not- rub potentially frostbitten areas, as there may be tiny ice crystals under the skin that will lacerate the layers underneath. If color does not return rapidly to the skin, place the affected part in warm, not hot, water. Dry it carefully and apply a light dressing without pressure. Do -not- burst any blisters. Raise the limb to reduce swelling and if necessary administer an oral pain relief.

Trader’s Foot

This may be caused by prolonged exposure to near-freezing temperatures in damp, slushy conditions. Lack of mobility, tight boots and wet clothing all increase the risk. In the early stages the feet are white, cold and numb. Later they become red, hot and very painful, with blisters sometimes forming. Treatment is as for frostbite.


This condition develops as the body temperature falls, the effects varying with the speed of onset and the level to which the temperature falls. Moderate hypothermia can usually be reversed. Deep hypothermia is often, though not always, fatal. It is always worth persisting with resuscitation for sometime.

It can be caused by prolonged exposure to cold outdoors, especially in wet and windy conditions. Moving air has a greater cooling effect and can substantially increase the risk. Cold water can also cause death from hypothermia rather than drowning. When surrounded by water, the body cools some twenty-five times faster than in air and a low body temperature can be reached in a relatively short time. As hypothermia develops there may be shivering, with the skin appearing cold, pale and dry. There may be apathy, confusion or irrational behaviour, lethargy and failing consciousness. Slow and shallow breathing, a weakening pulse and in extreme conditions cardiac arrest are other signs.

If you have brought the casualty indoors then they may be rewarmed quickly in a hot bath. The very young and very old should not be put straight into hot baths. Instead wrap them in blankets and gradually rewarm them. If you do not, rapid warming may send cold blood from the body to the heart and brain. Likewise, don't place hot articles next to the skin. Get the patient into bed, covering their head for extra warmth. Conscious patients can be fed warm drinks, although the attending Healer may have to help them. Drinks should be sweet and high-energy, for example sweetened klah. Someone should stay with the patient until color and warmth returns to their skin.

Effects of Extreme Heat

In extremely hot conditions, the body's heat-loss mechanisms may fail. For example, when the air is laden with moisture (high humidity), sweat does not evaporate well. In these circumstances, particularly during strenuous exercise, when extra heat is generated by muscular activity, heat exhaustion, or the more dangerous condition heatstroke, may develop.

Prickly Heat

Prickly heat is a highly irritating, prickly red rash caused by inflamed glands in the skin and occurs particularly in areas not well-aerated. Sufferers are likely to succumb to heatstroke unless the condition is corrected. Check on their personal hygiene and advise them to wear clean, loose clothing of cotton or sisal. They should spend as much time as possible in cool conditions and avoid exercise in the heat.

Heat Exhaustion

This condition usually develops gradually and is caused by the loss of salt and water from the body by excessive sweating. It is more common in people unaccustomed to working or exercising in a hot, humid environment and in those who are unwell, especially those with diarrhea and vomiting. As the condition develops there may be headaches, dizziness, confusion, loss of appetite, nausea, and cramps in the limbs or lower abdomen. Sweating may also be present with pale clammy skin and a rapid, weakening pulse and breathing.

Move the patient to cool surroundings, getting them to lie down and raise their legs, which will improve the blood flow to the brain. Providing they are conscious help them to sip plenty of weak salt solution.

Heat Stroke

This condition often occurs suddenly and can cause unconsciousness in minutes. There may be a warning period in which the casualty feels uneasy and unwell. It can be caused by prolonged exposure to hot surroundings or by a fever. Headaches, dizziness and discomfort are all signs. Also a hot, flushed and dry skin may be present, with a rapid deterioration in the level of response to stimuli. Additionally, a full bounding pulse may be detected. Move the casualty to a cool place and remove all outer clothing. Wrap them in a cold, wet sheet and keep it wet. When the temperature has fallen to more normal levels, replace the wet sheet with a dry one and keep a close check on them. If the temperature begins to rise once more, repeat the cooling process.

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