Physical Urticaria: Types, Mechanisms, and Management

Definition

Physical urticaria (physical allergy) comprises a heterogeneous group of conditions where hives (wheals) and/or angioedema are reproducibly triggered by specific physical stimuli—without allergen-specific IgE involvement.

Common Subtypes

Subtype	Trigger	Key Features
Dermatographism	Firm stroking/scratching	Most common; linear wheals appear within minutes; "skin writing"
Cold urticaria	Cold air, water, objects	Wheals on rewarming; risk of anaphylaxis with swimming; ice-cube test diagnostic
Cholinergic urticaria	Heat, exercise, stress	Small (1–3 mm) punctate wheals; triggered by core temperature rise
Solar urticaria	UV/visible light	Rare; wheals within minutes of exposure; action spectrum varies
Pressure urticaria	Sustained pressure	Delayed (4–6 h), deep, painful swelling; palms, soles, buttocks
Vibratory urticaria	Vibration	Rare; genetic forms (ADGRE2 mutation) identified
Aquagenic urticaria	Water contact	Very rare; wheals regardless of temperature; mechanism unclear
Heat urticaria	Local heat	Rare; wheals at site of heat application

Pathophysiology

Mast cell degranulation via non-IgE pathways (complement, neuropeptides, direct physical activation). Histamine, prostaglandins, leukotrienes cause vasodilation, edema, sensory nerve stimulation.

Diagnosis

• Detailed history + provocation testing (ice cube, pressure device, light box, exercise challenge)
• Exclude chronic spontaneous urticaria and systemic diseases

Management

1. Avoidance of identified triggers
2. Second-generation H1-antihistamines (cetirizine, loratadine, fexofenadine) up to 4× standard dose
3. Omalizumab (anti-IgE) for refractory cases
4. Short-course corticosteroids for acute flares
5. Phototherapy (UVB) for solar urticaria