What should you know about transient heat fatigue?

Transient heat fatigue is temporary tiredness after heat exposure, often linked to fluid loss, overheating, or physical exertion. It should improve with cooling, rest, and appropriate fluids; symptoms that persist or become severe need medical review.

Heat can make the body work harder to regulate temperature. Sweating removes fluid and salts, while exertion, humid air, poor sleep, or illness can add to the strain. You may notice weakness, headache, dizziness, thirst, muscle cramps, nausea, or difficulty thinking. Dehydration is a common concern, but fatigue can also accompany infections such as COVID-19 or conditions such as anaemia.

If tiredness continues after you are cool and hydrated, or returns without heat exposure, a clinician may consider other explanations including burnout, chronic fatigue syndrome, kidney disease, coeliac disease, or alcohol-related health problems.

Move to shade or an air-conditioned place, loosen excess clothing, rest, and cool the skin with a fan or damp cloth. Sip suitable fluids regularly; if you have been sweating heavily, ask a pharmacist or clinician whether an oral rehydration drink is appropriate. Avoid strenuous activity until you feel recovered, and never leave a tired or confused person in a hot car or closed room. Resume activity gradually.

Get emergency help for confusion, fainting, a seizure, severe weakness, trouble breathing, inability to drink, or very hot skin with worsening illness. Seek medical advice promptly if vomiting prevents fluids, urine becomes very dark or sparse, or symptoms do not improve after cooling and rest. People who are pregnant, older, very young, or living with long-term illness may need earlier advice.

Ask how much activity and fluid intake are suitable for you, whether medicines increase heat sensitivity, and whether persistent fatigue needs blood tests or another assessment. Mention recent heat exposure, sweating, illness, sleep, and any change in urination.