Fatigue from heat: what to know

Your body sends more blood towards the skin and produces sweat to release heat. Sweating removes water and salts, while heat can make physical and mental effort feel harder. Early heat stress may cause tiredness, thirst, headache, dizziness, nausea, muscle cramps or heavy sweating. Dehydration is more likely after outdoor activity, fever, vomiting or diarrhoea, and can be more concerning for people with kidney disease.

Heat is not the only possible explanation for ongoing fatigue. Anaemia, COVID-19, coeliac disease, burnout and other conditions can also present with tiredness. Alcohol can worsen fluid loss and sleep quality. A pattern that continues in cooler conditions deserves a clinical review.

Stop exertion and move into shade or an air-conditioned place. Loosen clothing, use cool wet cloths, and sip water regularly. If you have been sweating heavily, a suitable oral rehydration drink may help replace salts; follow medical advice if you have kidney or heart disease. Avoid alcohol and strenuous activity until you feel recovered. Reschedule outdoor work for a cooler part of the day and use light clothing, shade and planned breaks.

Call emergency services if someone is confused, collapses, has a seizure, cannot drink, becomes unusually drowsy, or has very hot skin with worsening illness. Do not leave an unwell person alone. Seek medical advice if dizziness, vomiting, weakness or a rapid heartbeat does not settle after cooling and fluids, or if fatigue keeps returning.

Ask whether medicines, kidney problems, anaemia or another illness could increase your sensitivity to heat. Share your fluid intake, sweating, urine changes, recent infection, alcohol use and the setting in which symptoms began.