Health effects of heat

Sweating helps release heat, but heavy sweating also removes fluid and salts. Dehydration may cause thirst, a dry mouth, headache, dizziness, dark urine and tiredness. Heat exhaustion can bring weakness, nausea, cramps, clammy skin and feeling faint. Heatstroke is a medical emergency: the person may become confused, unusually drowsy, unsteady or have a seizure, and the skin may feel very hot. Infants, older adults, pregnant people, and those with heart, lung or kidney problems can become unwell sooner. Some medicines can also affect sweating, fluid balance or blood pressure.

Move to a cool or shaded place, loosen extra clothing and sip cool water if you are awake and able to swallow. A cool shower, damp cloths or a fan can help. Avoid strenuous activity during the hottest part of the day, take regular breaks, wear loose light clothing and check on people who may struggle to recognise or communicate thirst. Do not stop prescribed medicine without medical advice; ask a pharmacist how heat and your medicines may interact.

Call emergency services if someone is confused, has a seizure, collapses, cannot drink, or remains very hot and unwell after cooling. Do not give fluids to an unconscious or confused person. Seek prompt medical advice for persistent vomiting, fainting, worsening weakness, or symptoms that do not improve after resting in a cool place.

Could my health conditions or medicines increase my risk in hot weather? How should I adjust fluids, activity and monitoring during a heatwave? What symptoms should prompt me to seek urgent help?