What causes heat intolerance?

Heat intolerance means feeling unusually uncomfortable or becoming unwell in warm surroundings. Heavy sweating, flushing, tiredness, headache, dizziness, nausea, or a fast heartbeat can occur. The symptom can be temporary after fever, vomiting, diarrhoea, or not drinking enough fluid.

Some medicines can make heat harder to tolerate by reducing sweating, increasing fluid loss, or affecting blood pressure. Examples include some antihistamines, antidepressants, diuretics, and medicines used for bladder symptoms; do not stop a prescribed medicine without medical advice. An overactive thyroid can increase heat sensitivity along with sweating, tremor, palpitations, anxiety, or unexplained weight loss. Higher body weight and some long-term illnesses may also make cooling less efficient.

Move to a cool, well-ventilated place, loosen extra clothing, and drink fluids regularly unless a clinician has told you to restrict them. Use cool damp cloths or a lukewarm shower, and avoid strenuous activity during the hottest part of the day. Keep a note of when symptoms begin, what you were doing, your fluid intake, and every medicine or supplement you take. Arrange a routine appointment if the problem keeps returning, is worsening, or began after a medicine change; a clinician may review your medicines and check for thyroid, hormonal, or other causes.

Seek urgent medical help for confusion, fainting, a seizure, severe weakness, trouble breathing, chest pain, or loss of consciousness after heat exposure. Hot, dry skin, a very high body temperature, or symptoms that do not improve promptly after cooling can signal heatstroke. Heat exhaustion can cause heavy sweating, weakness, headache, dizziness, and nausea; it needs prompt cooling and medical assessment if it is severe or does not settle.

Ask: Could any of my medicines or supplements affect sweating or fluid balance? Do my other symptoms suggest a thyroid or hormonal problem? Should I have blood tests or a medication review? What warning signs should prompt urgent help, and how much fluid is suitable for me?