heat illness

Last edited 08/2022 and last reviewed 08/2022

Heat illness

UK definition of heatwave

  • a heatwave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold
    • threshold varies by UK county
  • see https://www.metoffice.gov.uk/ for details

People over 65, pregnant women, infants, young children, athletes, outdoor workers, those living in urban environments, patients with comorbidities, and those on certain medications are particularly at risk of heat related illness (1)

Heat stroke is the most evident manifestation of heat illness, but more concerning is that heat exposure can exacerbate existing long term conditions, including cardiovascular, pulmonary, and renal disease, and mental illnesses (1)

Heat stroke has been classified into two groups according to the presence or absence of exertion (2)

  • exertional heat stroke
    • develops in able-bodied individuals, such as athletes, soldiers, or laborers, and performing rigorous physical activities
  • nonexertional heat stroke
    • can develop during low-level physical activities among elderly, ambulatory individuals with comorbidities including obesity, diabetes, hypertension, heart disease, renal disease, dementia, and alcoholism
  • has been defined as (3):
    • as a core body temperature that rises above 40 degrees C, accompanied by hot dry skin and central nervous system abnormalities, such as delirium, convulsions, or coma.
    • also proposed an alternative definition of heat stroke on the basis of its pathophysiology, stating that heat stroke is a form of hyperthermia associated with a systemic inflammatory response that leads to a syndrome of multiorgan dysfunction, predominantly encephalopathy
  • heat stroke progresses to multiorgan dysfunction syndrome; therefore, rapid, effective cooling followed by close monitoring and specific treatment for injured organs are fundamental to treatment success (2)



  • Sorensen C, Howard C, Prabhakaran P, Horton G, Basu R. Heat illnesses in clinical practice BMJ 2022; 378 :e070762 doi:10.1136/bmj-2022-070762
  • Hifumi T, Kondo Y, Shimizu K, Miyake Y. Heat stroke. J Intensive Care. 2018 May 22;6:30. doi: 10.1186/s40560-018-0298-4.
  • Bouchama A, Knochel JP. Heat stroke. N Engl J Med. 2002;346:1978-1988