Fainting from heat: what to know

Hot surroundings make the body send more blood toward the skin to release heat. Sweating also removes fluid and salt. Standing still, rising quickly, illness, alcohol, or not drinking enough can make blood pressure fall further. Warning symptoms may include light-headedness, nausea, blurred vision, weakness, clammy skin, or ringing in the ears before a brief loss of consciousness.

Fainting itself is a symptom, not a diagnosis. Dehydration can contribute, while anaemia, low blood sugar, or an irregular heartbeat may also need consideration if episodes recur or occur away from heat.

Lay the person flat on their back in a cool place and raise their legs. Loosen tight clothing, use cool wet cloths or airflow, and check that they are breathing normally. Do not give food or drink until they are fully awake and able to swallow. Once alert, small sips of water may help if there is no vomiting and a clinician has not restricted fluids. Have them rest before standing slowly.

Call emergency services if the person does not wake quickly, has trouble breathing, chest pain, a severe headache, a seizure, an injury, confusion, or an abnormal heartbeat. Urgent assessment is also needed after fainting during exercise, while lying down, or more than once. Arrange medical review for a first unexplained episode, repeated dizziness, or fainting despite cooling and fluids.

Ask whether medicines, blood pressure, heart rhythm, anaemia, or glucose could have contributed. Bring the sequence of symptoms, the setting, fluid intake, recovery time, and any family history of sudden heart problems.