Head > Heat Illness

What is Heat Illness?

Heat illness generally falls into three progressively more serious categories:

   Heat (or muscle) cramps

   Heat exhaustion

   Heat stroke

There is overlap between the three; for example, cramps can be present in all three forms of heat illness. Heat cramps usually affect the lower legs and abdominal muscles. Heat exhaustion occurs when the body’s cooling system (mainly perspiration) is unable to keep up with heat stress. Without treatment, this condition can soon progress to heat stroke. Heat stroke is a medical emergency in which the body’s cooling systems suddenly shut down. It can lead to severe dehydration and hyperthermia (a dangerous elevation of body temperature) which can cause damage to the brain and other organs. Heat stroke can be fatal if not treated quickly by health-care professionals. Young children, senior citizens and those in poor general health are especially susceptible to heat illnesses.

Heat illness is caused by an imbalance between water and electrolytes (such as sodium, potassium, and calcium). Muscle cramps also can be caused by the buildup of lactic acid in the muscle that can occur during strenuous exercise. When you get dehydrated, there is not enough blood flow to the leg muscles, and the muscles' balance of water and electrolytes (salts) is upset, so the muscles tighten up into a cramp, usually affecting the lower legs and abdominal muscles.

The most important thing to do when having to exercise on a hot, humid day is to drink plenty of fluids. You cannot rely on your body's thirst-feedback mechanism to know how much to drink. If you are in a low humidity area, when you perspire, it will help you cool off more, so you can tolerate higher temperatures better in a dry climate. You need to drink about a quart of fluid for every pound of body fluid you lose during exercise. Drink water at least every 15 minutes on hot, humid days. Try to plan your activities early in the morning or late in the afternoon to avoid exposure during the hottest hours of the day. Know when to say “no” to exercise. You should be drinking enough water so that your urine is light-colored and not dark yellow. That can be an indicator of your level of hydration. Because caffeine and alcohol can cause you to lose extra fluid, they should be avoided. Wearing a hat or sun visor, particularly one that can “breathe,” helps protect you from the effects of direct sunlight. A football helmet is not designed for heat loss. You should also try to wear loose-fitting clothing made from a breathable material, such as cotton, and go for light colors, which do not absorb as much sunlight. Athletes in stadiums, especially those with artificial-turf surfaces, are even more susceptible to heat illness. Because much body heat is lost through the head, pouring cool water over the head and scalp can promote heat loss and help prevent heat injury.

Treatment of heat-related muscle cramps associated with heat exhaustion includes ceasing strenuous activity and retreating to a cooler place; stretching and then massaging of afflicted muscle groups, followed by icing; and replenishment of fluids with water, sports drink, or fruit juice. For heat exhaustion, treatments include immediate relocation to a cool place; removal of excess clothing; sponging or sprinkling the body with cool water, and copious replenishment of fluids. Medical assistance may be required. For heat stroke, immediate treatments include either cool baths or ice packs near large arteries such as at the neck and armpits, and oral or intravenous replenishment of fluids. If in doubt, seek urgent medical assistance. Heat stroke is a medical emergency.