When to worry about dark urine with heat exhaustion

Sweating reduces the fluid available to the body, so the kidneys conserve water and urine becomes concentrated and darker. Heat exhaustion may also cause heavy sweating, thirst, headache, nausea, weakness, dizziness, and clammy skin. Dark urine after strenuous heat exposure can also signal muscle injury, particularly with severe muscle pain or unusual weakness.

Stop activity, move into shade or air conditioning, loosen excess clothing, and cool the skin with wet cloths or a fan. Sip water or an oral rehydration drink if you are awake and able to swallow. Have someone stay with you and avoid returning to heat until fully recovered.

Get medical advice if dark urine continues, you are urinating very little, or weakness, cramps, nausea, or dizziness persists after cooling and drinking. Call emergency services for confusion, collapse, seizure, loss of consciousness, severe breathing trouble, or very hot skin with altered behaviour.

Ask how to plan fluids and breaks during hot work or exercise, whether your medicines increase heat risk, and whether persistent dark urine needs kidney or muscle testing.