Heat-related illness

Last revised by Daniel J Bell on 4 Sep 2022

Heat-related illnesses are on the increase due to increasing global temperatures. The normal physiological response to excessive heat is known as heat stress and although uncomfortable is generally not considered pathological. If this is not alleviated, then a true heat illness may result, which may be mild, e.g. heat cramps, moderate, e.g. heat exhaustion, or rarely severe and life-threatening as heat stroke.

It is important to recognize that as serious as heat stroke is, more of the healthcare burden from increased temperatures is from the heat aggravating pre-existing morbidity, including cardiovascular, respiratory and renal disease. It is clear that during and following spells of hotter weather, all-cause morbidity and mortality rapidly rises 3.


  • heat wave
    • any two days plus period of weather hotter than would normally be expected for that locale - precise definitions vary from country to country
  • heat stress
    • uncomfortable physiological state due to a hot environment, particular if performing physical labor
  • mild heat illness
    • heat rash (a.k.a. prickly heat)
      • an uncomfortable epidermal inflammation due to obstructed sweat glands +/- superadded staphylococcal infection
    • heat cramps
      • painful muscular spasms in the midst of, or post exertion, usually resulting from sweat-related salt loss from hard labor in a hot climate
  • moderate heat illness
    • heat syncope
      • dizziness and/or loss of consciousness commonly from standing still for long durations in heat
    • heat exhaustion
      • mild to moderate illness due to water and/or salt loss +/- abnormal core temperature, with mild CNS disturbance and systemic effects
  • severe heat illness
    • heat stroke
      • high fatality condition with core temperature >40°C and CNS dysfunction, e.g. confusion, seizures, coma
      • hyperthermia, a loss of normal homeostatic ability to maintain normal core temperature, is a component of heat stroke


Risk factors

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