Delayed onset heat exhaustion: what to know

Sweating lowers body water and salts, while exertion and hot surroundings increase the strain on temperature control. You may feel unwell later, after entering a cool room or stopping activity. Possible features include weakness, headache, nausea, dizziness, thirst, clammy skin, heavy sweating, muscle cramps, and darker urine. These symptoms can overlap with dehydration. Heat exhaustion is different from heatstroke, which can involve confusion, collapse, seizures, or a very hot body and is an emergency.

Stop exertion and move to shade or air conditioning. Loosen extra clothing, cool the skin with damp cloths or a fan, and rest lying on your side if nausea makes sitting difficult. If you are awake and can swallow, take frequent small sips of water or an oral rehydration drink. Avoid alcohol and strenuous activity until you feel fully recovered. Do not force fluids if you are vomiting, confused, or too drowsy to drink safely.

Call emergency services for confusion, fainting, seizure, severe weakness, trouble breathing, inability to drink, repeated vomiting, or worsening symptoms despite cooling. A very hot body, loss of normal sweating, or unusual behaviour may indicate heatstroke. Seek medical advice promptly if symptoms recur, urine remains very dark, or you have a condition or medicine that affects fluid balance. Do not return to exercise simply because sweating has stopped.

Ask: Could this be dehydration or another problem? How should I replace fluids and salts? When is it safe to work or exercise in heat again? Could my medicines increase heat illness risk? What symptoms mean I should seek emergency help?