Definition
Heat urticaria is a subtype of physical urticaria in which exposure to elevated temperatures—whether from ambient heat, direct contact with hot objects, or localized warming—induces transient, pruritic wheals (hives) on the skin. The reaction typically resolves within a few hours after the triggering heat stimulus is removed.
Overview
Heat urticaria belongs to the broader group of physical urticarias, conditions in which physical stimuli provoke mast‑cell degranulation and the release of histamine and other inflammatory mediators. The disorder may occur alone (idiopathic) or in association with other chronic urticarias. Episodes are often episodic, and the severity can vary according to the intensity and duration of heat exposure. Diagnosis is primarily clinical and is confirmed by reproducible provocation tests that involve controlled heating of a small skin area.
Etymology / Origin
The term combines “heat,” derived from Old English hǣtu meaning “warmth,” with “urticaria,” from Latin urtica (nettle) and the Greek ὄρτυξ (ortux), referring to the nettle‑like rash characteristic of the condition. The phrase “heat urticaria” therefore literally denotes a nettle‑like rash caused by heat.
Characteristics
| Feature | Description |
|---|---|
| Trigger | Exposure to temperatures generally above 40 °C (104 °F); can be whole‑body (e.g., hot climate) or localized (e.g., hot water, heating pad). |
| Latency | Onset typically within minutes (often 5–30 min) after heat exposure. |
| Lesion morphology | Raised, erythematous, edematous wheals ranging from a few millimetres to several centimetres; may coalesce into larger plaques. |
| Symptoms | Intense itching, burning, or stinging sensation; occasional mild swelling of the affected area. |
| Duration | Individual wheals usually resolve within 1–4 hours after removal of the heat source; recurrent episodes may persist for years. |
| Diagnostic tests | Heat provocation test (e.g., application of a warm metal probe or heated water at a defined temperature for a set time) reproduces lesions; skin biopsy is not routinely required. |
| Differential diagnosis | Other physical urticarias (cholinerigic, cold, pressure), contact dermatitis, erythema multiforme, and heat‑induced burns. |
| Management | • Avoidance of known heat triggers; • Use of antihistamines (second‑generation H1 antagonists) for symptom control; • In refractory cases, leukotriene receptor antagonists or omalizumab may be considered; • Patient education on safe temperature limits. |
| Prognosis | Many patients experience gradual improvement or remission over time; however, some retain lifelong sensitivity to heat. |
Related Topics
- Physical urticaria – A classification of urticarias triggered by physical factors such as cold, pressure, vibration, or sunlight.
- Cholinergic urticaria – A heat‑related urticaria precipitated by increased body temperature from exercise or emotional stress.
- Dermatographism – A form of physical urticaria elicited by mechanical stroking of the skin.
- Urticaria multiforme – A pediatric variant of acute urticaria with annular lesions, distinct from heat‑induced forms.
- Antihistamine therapy – The primary pharmacologic approach for managing urticarial reactions.
- Omalizumab – An anti‑IgE monoclonal antibody used for chronic spontaneous urticaria and sometimes for refractory physical urticarias.