What causes urticaria in children?

Causes of Urticaria in Children

Urticaria in children is most commonly caused by infections (especially viral and urinary tract infections), followed by physical factors, foods, medications, and autoimmune processes, though many cases remain idiopathic despite thorough evaluation. 1, 2

Main Causes of Urticaria in Children

Acute Urticaria (lasting less than 6 weeks)

• Infections (48.6% of cases) 3

  • Viral infections (most common trigger)
  • Urinary tract infections
  • Chlamydia pneumoniae infections
  • Helicobacter pylori infections
  • Dental abscesses (though evidence is limited) 1

• Medications (5.4% of cases) 3

  • Antibiotics
  • NSAIDs and aspirin
  • Codeine and other direct mast cell degranulators 1
  • Radiocontrast media 1

• Food allergies (2.7% of cases) 3

  • IgE-mediated reactions to environmental allergens (nuts, fish, latex) 1
  • Dietary pseudoallergens (salicylates, azo dyes, food preservatives) 1

Chronic Urticaria (lasting more than 6 weeks)

• Physical factors (52.9% of cases) 3

  • Dermatographism
  • Delayed pressure urticaria
  • Cold-induced urticaria
  • Heat-induced urticaria
  • Cholinergic urticaria (triggered by sweating)
  • Solar urticaria
  • Aquagenic urticaria 4

• Autoimmune causes

  • Thyroid autoimmunity (14% of chronic urticaria vs. 6% in controls) 1, 4
  • Functional autoantibodies against high-affinity IgE receptor or against IgE (approximately one-third of chronic cases) 2

• Associated conditions

  • Celiac disease (higher prevalence in children with severe chronic urticaria) 1
  • Helicobacter pylori infection 1, 4

Special Considerations

Urticaria with Systemic Involvement

• Urticarial vasculitis (presents with urticaria clinically but shows small vessel vasculitis histologically) 1
• Autoinflammatory syndromes (typically present in early childhood with spontaneous weals, fever, and malaise) 1
• Systemic-onset juvenile idiopathic arthritis 5

Diagnostic Clues from Weal Duration

• Ordinary urticaria: weals last 2-24 hours
• Contact urticaria: weals last up to 2 hours
• Physical urticaria: weals disappear within an hour (except delayed pressure urticaria)
• Urticarial vasculitis: weals persist for days 1

Diagnostic Approach

The diagnosis of urticaria is primarily clinical, and investigations should be guided by the history rather than performed routinely in all patients 1, 4.

For acute urticaria:

• No investigations are required except where suggested by the history
• IgE-mediated reactions can be confirmed by skin-prick testing or CAP fluoroimmunoassay 1

For chronic urticaria not responding to antihistamines:

• Full blood count and white cell differential
• Erythrocyte sedimentation rate
• Thyroid autoantibodies and thyroid function tests 1, 4

Prognosis

• Acute urticaria generally has a favorable prognosis 6
• Chronic urticaria has a resolution rate of approximately 50% within 6 months 4

Pitfalls and Caveats

• Urticaria with angioedema must be differentiated from hereditary angioedema (C1 esterase inhibitor deficiency), which requires different management 1, 5
• Chronic urticaria is rarely due to an external cause, despite patients' and parents' concerns 6
• Mastocytosis can mimic chronic urticaria and requires different treatment approaches 5
• Anaphylaxis must be ruled out in acute presentations with systemic symptoms 7

Understanding the diverse causes of urticaria in children is essential for appropriate management and for providing reassurance to concerned families, particularly since many cases will resolve spontaneously over time.