What should you know about body heat causing hives?

This reaction may cause raised, itchy welts that appear as the body warms and fade as the skin cools. It is often called heat-induced or cholinergic urticaria. Hot weather, a fever, vigorous activity, emotional stress and warm showers can all raise skin temperature. The rash may affect the trunk, arms, neck or other areas and can come and go in separate episodes. Swelling deeper in the skin is called angioedema and may affect the lips, eyelids, hands or feet.

A clinician may ask what you were doing before the welts appeared, how quickly they spread, and whether breathing, swallowing or the voice changed. A photograph taken during an episode can help if the skin has cleared before the appointment.

Move to a cooler place, loosen tight clothing and use a cool, damp cloth rather than scratching or applying ice directly. Sip fluids, pause exercise and avoid very hot showers until the episode settles. Choose breathable clothing and notice triggers such as heat, sweat, alcohol or spicy foods. A pharmacist or clinician can advise whether an oral antihistamine treatment is suitable for you; do not take someone else’s prescription or exceed the label directions. Recurrent episodes deserve a medical assessment so other causes of hives can be considered.

Seek emergency help immediately for trouble breathing, wheezing, throat or tongue swelling, faintness, confusion, or difficulty swallowing. These symptoms can signal a serious allergic reaction even if the skin rash seems small. Arrange prompt medical advice when hives keep returning, last longer than expected, interfere with sleep or activity, or occur with marked swelling. A clinician may discuss antihistamines and, for selected severe episodes, oral corticosteroid treatment.

Could this be heat-triggered urticaria, and what other causes should be checked? Which symptoms mean I should seek emergency help? What medicine is appropriate with my health conditions, pregnancy or breastfeeding status? Should I keep a heat, activity and food symptom diary?