Key Facts

Urticaria is extremely common, affecting ~15–20% of the population at some point. The key clinical distinction is acute vs chronic, as this determines investigation and management approach.

Epidemiology

• Lifetime prevalence: ~15–20%
• Acute urticaria: very common, especially in children
• CSU: prevalence ~0.5–1%; female:male 2:1; peak age 20–40 years
• CSU duration: median 2–5 years; ~50% resolve within 5 years

Aetiology

Acute: viral infection (commonest cause in children), drugs (NSAIDs, antibiotics, opioids), food (nuts, shellfish, egg), insect stings, latex Chronic spontaneous: autoimmune (~50%; autoantibodies to FcεRI or IgE), idiopathic (~50%); NOT food allergy Physical: dermatographism (most common physical urticaria), cold, cholinergic, pressure, solar, aquagenic

Pathophysiology

• Mast cell degranulation → histamine, leukotrienes, prostaglandins → vasodilation, increased vascular permeability → wheal formation
• Autoimmune CSU: IgG autoantibodies to high-affinity IgE receptor (FcεRI) on mast cells → chronic activation
• Physical urticarias: specific physical stimulus triggers mast cell degranulation

Typical Wheals

• Raised, erythematous, pruritic
• Variable size (mm to cm)
• Individual wheals resolve within 24 hours leaving normal skin
• Flare-and-wheal response

Angioedema

• Deep tissue swelling (lips, eyelids, tongue, hands, feet, genitalia)
• May accompany urticaria (~40% of CSU patients)
• Lasts 24–72 hours

Physical Urticarias

• Dermatographism: linear wheals from stroking/scratching skin
• Cold urticaria: wheals after cold exposure; risk of anaphylaxis in cold water
• Cholinergic: small 2–3mm wheals after exercise, heat, emotional stress

Red Flags

• Anaphylaxis (urticaria + hypotension, bronchospasm, airway compromise)
• Wheals lasting >24 hours (urticarial vasculitis)
• Angioedema without urticaria (consider hereditary angioedema — C1-INH deficiency)
• Wheals that leave bruising/purpura

Acute Urticaria

• Usually NO investigations needed — clinical diagnosis
• Consider allergy testing (specific IgE, skin prick test) if clear trigger suspected and future avoidance needed

Chronic Spontaneous Urticaria

• FBC + differential: eosinophilia (parasites), basopenia
• CRP/ESR: raised in urticarial vasculitis, autoinflammatory
• TFTs: thyroid autoimmunity associated with CSU (~10%)
• Total IgE: may help predict omalizumab response
• Autologous serum skin test (ASST): research tool for autoimmune CSU
• Extensive allergy testing NOT recommended in CSU

If Urticarial Vasculitis Suspected

• Skin biopsy: leucocytoclastic vasculitis
• Complement (C3, C4): low in hypocomplementaemic urticarial vasculitis (association with SLE)
• ANA, anti-dsDNA: if SLE suspected

Acute Urticaria

• Identify and avoid trigger if clear
• Non-sedating antihistamine: cetirizine 10mg OD, loratadine 10mg OD, or fexofenadine 180mg OD
• Short course oral prednisolone: 30–40mg for 3–5 days for severe acute urticaria/angioedema
• Adrenaline IM: if anaphylaxis

Chronic Spontaneous Urticaria (Stepwise — EAACI/BAD)

Step 1: Standard-dose non-sedating antihistamine (e.g. cetirizine 10mg OD) Step 2: Up-dose to 4× licensed dose (e.g. cetirizine 10mg QDS) — first escalation Step 3: Add omalizumab 300mg SC every 4 weeks (anti-IgE monoclonal — NICE TA339) Step 4: Add ciclosporin 3–5mg/kg/day (off-label; specialist only)

• Avoid: oral corticosteroids long-term; sedating antihistamines as maintenance
• LTRA (montelukast): weak evidence; can be tried as add-on

Physical Urticarias

• Non-sedating antihistamines (may need higher doses)
• Avoidance of specific trigger where possible
• Cold urticaria: desensitisation protocols (specialist)

Referral Criteria

• Dermatology/allergy: CSU not controlled with standard antihistamines
• Immunology: suspected hereditary angioedema
• Urgent: anaphylaxis, wheals >24h (biopsy for urticarial vasculitis)

• Acute urticaria: self-limiting in most cases (days to weeks)
• CSU: median duration 2–5 years; ~50% resolve within 5 years; ~20% persist >10 years
• Omalizumab: ~65–70% achieve good control (UAS7 ≤6)
• Autoimmune CSU: may have longer duration
• Physical urticarias: often persistent but manageable with antihistamines
• QoL: significant impact; comparable to coronary artery disease in some studies

CSU Treatment Stepladder

Urticaria Activity Score (UAS7)