An Overview of Heat Stress

Heat stress is a condition that occurs when the body is unable to regulate its internal temperature and cool itself through sweating. Heat stress shows many symptoms and encompasses several heat-induced illnesses such as heat stroke, heat exhaustion, heat cramps and heat rashes. These conditions are more likely to occur during hot summer months, but may affect workers and athletes in various climates and conditions year round. The most common composite measurement used to determine appropriate exposure to heat stress conditions is Wet Bulb Globe Temperature or “WBGT."

Different Types of Heat Stress

Non-exertional heat stroke is caused by just being in a hot environment which leads to rise in body temperature. Exertional heat stroke is caused by intense physical activity which also leads to an increase in body temperature. Working or exercising in hot or humid weather can lead to exertional heat stroke.

Exertional heat stroke is a medical emergency that could potentially lead to a life-threatened condition if not treated properly on-site.  Exertional heat stroke occurs when the body temperature reaches above 105°F with central nervous dysfunction such as confusion, disorientation, seizures, or irrational behavior.

Non-exertional vs. Exertional Heat Stroke:
Non-exertional (or classic) heat stroke usually occurs in elderly, infants, or patients with congenital disease who may be at a disadvantage in regulating the body temperature from heat stress.  Unlike exertional heat strokes, non-exertional heat strokes are prevalent in sedentary population and may occur without strenuous physical activity.

Heat Exhaustion
Heat exhaustion occurs when your body is unable to continue exercise due to heat stress. Often this is accompanied by dehydration. There are two kinds of heat exhaustion; water depletion, signs of which include excessive thirst, weakness, headache and loss of consciousness and salt depletion, signs include nausea and vomiting, muscle cramps and dizziness.

Heat Syncope
Syncope is the medical term for fainting. Heat syncope is fainting as a result of overheating and occurs alongside a sudden change in posture or sudden stop in exercise. It occurs when water is evaporated from the blood, which lowers the blood pressure further. Dehydration is a factor that contributes to heat syncope.

Heat Cramps
Heat cramps are muscle spasms that result from a large amount of salt and water loss during strenuous activity. Often they do not occur until after the activity, such as at night or when relaxing. Heavy sweating can cause heat cramps, particularly when water is replaced, but not salt or potassium.

Heat Rash
Heat rash is a skin irritation that can be caused by excessive sweat. A heat rash happens with sweat ducts become clogged and sweat cannot be released on the surface of the skin. It becomes trapped beneath the skin’s surface causing a rash or a mild inflammation. Heat rash can also be called prickly heat or miliaria.

Signs and Symptoms of Exertional Heat Stroke*

  • Weakness
  • Fatigue
  • Nausea
  • Dizziness/Light-Headedness
  • Altered consciousness
  • Collapse, staggering, or sluggish feeling
  • Fainting
  • Profuse sweating
  • Irritability
  • Diarrhea
  • Chills
  • Increase in core body temperature, usually above 104°F/40°C rectal temperature
  • Pale complexion
  • Decreased muscle coordination
  • Hot and wet or dry skin
  • Headache
  • Sodium Loss
  • Hyperventilation
  • Rapid Pulse, low blood pressure, quick breathing

* Adapted from Korey Stringer Institute:

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