What is Urticaria?
Urticaria is a mast cell-driven inflammatory skin disease characterized by the rapid appearance of itchy wheals (hives), angioedema (deeper swelling), or both, with individual wheals typically resolving within 24 hours and angioedema lasting up to 72 hours. 1, 2
Core Clinical Features
The defining characteristics of urticaria include:
- Wheals (hives): Raised, itchy lesions with surrounding erythema that blanch with pressure and resolve without leaving marks
- Angioedema: Deeper swelling of the dermis and subcutaneous tissue, often non-pruritic, lasting up to 3 days
- Transient nature: Individual wheals disappear within 2-24 hours in ordinary urticaria 2
The diagnosis is primarily clinical - no laboratory tests are required to establish the diagnosis of urticaria itself 2.
Classification Framework
Urticaria is classified along two key dimensions:
By Duration:
- Acute urticaria: Symptoms lasting ≤6 weeks, affecting approximately 20% of the population at some point in life 3, 4
- Chronic urticaria (CU): Symptoms persisting >6 weeks, affecting 0.1-1.5% of the population 1, 5
By Trigger Pattern:
- Spontaneous urticaria: Wheals appear without definite external triggers
- Inducible urticaria: Reproducibly triggered by specific physical stimuli (cold, pressure, heat, vibration, water, sunlight, exercise) 1, 4
Key Distinguishing Features by Subtype
Duration of individual lesions is diagnostically critical 2:
- Ordinary urticaria: 2-24 hours
- Contact urticaria: Up to 2 hours
- Physical urticaria: Usually <1 hour (except delayed pressure urticaria: 2-6 hours to develop, up to 48 hours to fade)
- Urticarial vasculitis: Days (this is NOT true urticaria but a vasculitic mimic)
Important Clinical Caveats
Angioedema without wheals requires careful evaluation to exclude non-urticarial causes, particularly:
- ACE inhibitor-induced angioedema
- Bradykinin-mediated angioedema (C1 esterase inhibitor deficiency)
- These conditions have different pathophysiology and treatment approaches 1, 2
Urticarial vasculitis presents clinically like urticaria but shows small vessel vasculitis on biopsy - individual lesions persist for days rather than hours, which is the key clinical clue 2.
The most recent international guideline emphasizes that urticaria can manifest as stand-alone angioedema without wheals, though other causes must be excluded first 1. The inflammatory markers and demographics differ between angioedema with wheals versus angioedema alone (lower female predominance, different IgG anti-FcεRI patterns).