Hives from Being Hot: What to Know

This pattern is often called heat- or exercise-triggered urticaria. Small, raised spots may join into larger patches and can feel prickly or intensely itchy. They may appear after a hot shower, time in a warm room, physical activity, emotional stress or fever. The rash can fade after the skin cools, although episodes vary. Hives are different from a fixed rash that stays in one place and flakes or bruises. Swelling around the lips, eyelids or tongue can occur with hives and is called angioedema.

A photograph taken while the welts are visible and a note of heat, exercise, food, medicine and timing can help a clinician assess the pattern.

Move to a cooler place, loosen tight clothing and use a cool, damp compress. Avoid scratching, very hot showers and strenuous activity until the episode settles. Keep the skin gently moisturised and drink fluids if you have been sweating. A pharmacist or clinician can advise whether an oral antihistamine is suitable for you; do not combine medicines or exceed the label directions. If episodes recur, ask about a prevention plan and whether another trigger is present.

Get emergency help immediately for trouble breathing, wheezing, faintness, confusion, or swelling of the tongue or throat. Seek urgent assessment for rapidly worsening facial swelling, repeated vomiting or symptoms affecting several body systems. Arrange a medical review if the hives keep returning, last beyond the expected episode, leave bruising, or come with fever or feeling unwell.

Could this be heat-triggered urticaria, and should I be assessed for another cause? What should I do before exercise or a hot shower? Which antihistamine is appropriate with my medicines and health conditions? How should I respond if swelling reaches my mouth or throat?