Allergic emergencies

Urticaria and angioedema

Overview and approach

Urticaria is usually histamine-mediated; angioedema may be histaminergic or bradykinin-mediated.

  • Acute urticaria is under 6 weeks of symptoms; chronic spontaneous urticaria (CSU) is wheals on most days for 6 weeks or longer (1).
  • Acute wheals usually resolve within 1 to 2 days but can last up to 6 weeks; in CSU wheals can be large and persistent (1).
Assessment and clinical features

Airway symptoms, wheals, exposure, ACE-inhibitor use, recurrence and family history.

  • Acute triggers: foods, drugs, insects (relevant exposure usually 1 to 2 hours before the rash), infections (very common in children), physical factors (heat, exercise, cold, alcohol). NSAIDs sometimes trigger acute urticaria but not CSU (1).
  • Severe symptoms affecting sleep and function occur in uncontrolled CSU (1). Ask about ACE inhibitor use and family history for angioedema without wheals. Angioedema without wheals may be bradykinin-mediated (ACE inhibitor, hereditary C1 inhibitor deficiency).
Differentials and investigations

Most uncomplicated acute urticaria needs no extensive test battery; recurrent unexplained angioedema warrants selective complement/specialist testing.

  • Acute urticaria: skin prick or specific IgE tests are not usually required unless a specific allergen is suspected. CSU: allergy tests are not recommended and may be positive from coexisting sensitisation; blood tests only if an underlying condition is suspected (1).
Management and follow-up

Treat mechanism and severity, review medicines and arrange allergy follow-up where indicated.

  • Trigger avoidance or minimisation, plus non-sedating antihistamines; in CSU higher doses are usually needed. Short oral corticosteroid courses only occasionally (acute) (1). Biologics for severe CSU or lack of response to high-dose antihistamines (1). Specialist referral is recommended for CSU, and for acute urticaria only if an allergic trigger is suspected (1).
Red flags and clinical pearls

Tongue/laryngeal swelling needs urgent care. Bradykinin angioedema may not respond to standard antihistamine/steroid treatment.

  • Wheals with breathing difficulty, hypotension or vomiting after an exposure: treat as anaphylaxis (see the Anaphylaxis page).
References
  1. ASCIA: Checklist, Acute Urticaria and Chronic Urticaria (2025)

Last updated from Sen’s notes on 9 October 2026.