What causes heat exhaustion?

Hot weather, strenuous activity, crowded or poorly ventilated spaces, and heavy protective clothing can all increase heat load. Sweating removes water and salt from the body. Risk rises when a person cannot drink enough, has vomiting or diarrhoea, starts activity already dehydrated, or is not acclimatised to hot conditions. Some medicines and health conditions can affect sweating or fluid balance, so a clinician may need to review the wider context.

Common features include marked sweating, weakness, headache, dizziness, nausea, thirst and cool or clammy skin. Dark urine can support concern about dehydration, but symptoms overlap with other problems.

Stop the activity and move to shade or an air-conditioned place. Loosen extra clothing, cool the skin with damp cloths or a fan, and take small, frequent sips of water or an oral rehydration drink if the person is awake and able to swallow. Rest and avoid returning to heat until fully recovered. Do not give drinks to someone who is confused, vomiting repeatedly or unable to swallow.

Seek emergency help for confusion, fainting, seizures, loss of consciousness, very hot skin, trouble breathing or inability to drink; these can signal heatstroke or another emergency. Get medical advice if symptoms do not improve promptly after cooling and fluids, or if vomiting, severe weakness or persistent dizziness continues. A person with severe dehydration may need supervised treatment.

Ask what may have increased your risk, whether a medicine or health condition affects heat tolerance, and how to plan fluids and breaks for work or exercise. Mention the setting, duration of exposure, drinks taken, urine changes and every symptom.