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What IS "heat illness"?

Heat illness can vary from minor symptoms to life threatening conditions. Know the progression of signs and symptoms to prevent serious injury when exercising or performing in hot environments.

From the Field

What exactly is “heat illness”? Is it the same as heat stroke?

HPRC's Answer

You’ve undoubtedly heard of heat stroke. Heat illness includes heat stroke, but it is actually an umbrella term for a series of cumulative and progressing conditions that can occur as a result of prolonged exertion in or exposure to hot environments. Factors that contribute to increased risk for heat illness include dehydration, lack of acclimatization, poor physical fitness, overweight or obesity, skin disorders, medications or supplements, fever, and chronic disease. Although the terms “heat illness” and “heat injury” are often used interchangeably, they also are not the same. The Army is currently in the process of redefining and clarifying these terms. Minor heat illnesses include heat rash and heat cramps. Heat rash is the mildest form of heat illness and causes skin irritation such as itchiness or a prickly sensation. Heat cramps, the next stage of heat illness, can cause painful muscle spasms as a result of dehydration and/or excessive sweating in hot temperatures. If you begin to recognize any of these symptoms during exercise or exertion in the heat, or if you suspect that you’re becoming less tolerant, rest and recover, if possible in cooler temperatures. Apply cold cloths or cold water to directly to the skin, particularly to the head, neck and groin. Seek medical attention if symptoms are not relieved.

Major heat illnesses, as defined by AR40-501, include heat exhaustion, heat injury, and heat stroke. Heat exhaustion may cause headache, fatigue, dizziness, feeling faint, rapid pulse, nausea, cold skin, and/or heavy sweating and can usually be resolved quickly with recovery in a cool environment, if available. It is important to recognize these symptoms quickly to prevent progression of heat illness. Heat injury is a more severe heat illness. Symptoms may be similar to those of heat exhaustion, but at this stage organ damage can occur. Heat stroke is the most severe, and possibly life threatening, stage of heat illness and occurs when your core temperature continues to rise above 104° F. It is distinguished by injury to the brain, which may include symptoms of irrational behavior, extreme confusion, seizures, or unconsciousness. It is likely that you will not be able to care for yourself in this situation, which is why it is important to recognize early symptoms of heat illness.

If possible, use the buddy system during prolonged heat exertion, in case emergency medical attention is necessary, because permanent injury or death can occur. It’s also possible to develop heat illness if you’re overdressed in more moderate temperatures, so it’s important to always listen to your body and remove layers as necessary, even if you’re not in extreme heat. Heat exhaustion and heat stroke can be prevented by addressing early symptoms of heat illness, so learn the symptoms and watch for them in yourself and others in your company. Check out other HPRC resources on heat acclimatization and other ways to prevent heat illness.