What are the causes of urticaria in a one‑year‑old boy?

Causes of Urticaria in a One-Year-Old Boy

In a one-year-old boy, acute urticaria is most commonly triggered by viral infections, followed by food allergens (especially milk, eggs, nuts, fish), medications, and contact with chemicals or irritants; however, a specific cause remains unidentified in many cases (idiopathic urticaria). 1, 2

Common Triggers by Category

Infectious Causes

• Viral infections are the leading identifiable trigger of acute urticaria in young children, often presenting with generalized, large annular or geographic plaques that may be slightly raised. 1, 2
• The clinical features in infants reflect the peculiar structure of neonatal and infant skin, with lesions typically more widespread than in older children. 2

Food Allergens

• Common culprits include cow's milk, eggs, peanuts, tree nuts, fish, and shellfish—foods that are increasingly introduced during the first year of life. 3
• When an IgE-mediated food allergy is suspected based on temporal relationship to ingestion, confirm with skin-prick testing or specific IgE (CAP) assays, interpreting results in the clinical context. 3

Medications

• Drug reactions, particularly to antibiotics (e.g., penicillins, cephalosporins) and antipyretics, can provoke acute urticaria in this age group. 1
• Aspirin and NSAIDs should be avoided because they trigger mast-cell degranulation and can worsen urticaria. 3

Contact Exposures

• Latex, chemicals, and irritants (e.g., soaps, detergents, topical products) can cause contact urticaria, which resolves within 2 hours of exposure and is never spontaneous. 3, 1

Physical Stimuli

• Physical urticarias (dermographism, cold, heat, pressure) are uncommon in infants but should be considered if lesions appear reproducibly with specific triggers and resolve within 1 hour. 3, 1

Idiopathic Urticaria

• A substantial proportion of acute urticaria cases remain idiopathic despite thorough evaluation, meaning no specific trigger is identified even after detailed history and appropriate testing. 3, 1
• This is a diagnosis of exclusion and does not require extensive laboratory work-up in typical cases. 3

Red Flags: When to Consider Alternative Diagnoses

Autoinflammatory Syndromes

• If the child presents with recurrent wheals accompanied by fever and malaise, consider hereditary autoinflammatory syndromes such as Cryopyrin-associated periodic syndromes (CAPS, including Muckle-Wells syndrome) rather than ordinary urticaria. 4, 5
• These conditions are rare but important to recognize because they require specialized immunologic evaluation and targeted therapy. 4

Urticarial Vasculitis

• Wheals persisting beyond 24 hours that resolve with bruising or hyperpigmentation suggest urticarial vasculitis, which requires a lesional skin biopsy to confirm small-vessel vasculitis. 3
• Ordinary urticaria wheals last 2–24 hours and resolve without scarring. 3

Angioedema Without Wheals

• Isolated angioedema (especially if recurrent or involving the abdomen) should prompt evaluation for C1-esterase inhibitor deficiency (hereditary angioedema), starting with serum C4 screening. 3
• This is uncommon in infancy but can present with abdominal pain as the sole manifestation. 3

Diagnostic Approach

History and Physical Examination

• Detailed history should document:
  • Timing and duration of individual wheals (ordinary urticaria: 2–24 hours per wheal). 3
  • Recent viral illness, new foods introduced, medications given, and contact with potential irritants. 3, 1
  • Presence of fever, joint pain, or systemic symptoms (suggests autoinflammatory disease or vasculitis). 4
  • Aggravating factors: overheating, emotional stress, physical triggers. 3
• Physical examination should confirm typical transient wheals and assess for angioedema (present in ~40% of urticaria cases). 5, 6

Laboratory Testing

• Routine laboratory tests are not required for typical acute urticaria in a one-year-old unless the history suggests a specific trigger or systemic disease. 3, 1
• Allergy testing (skin-prick or specific IgE) is indicated only when the history points to a reproducible food or environmental allergen. 3, 1
• Avoid extensive work-ups in straightforward acute urticaria; they do not add clinical value and delay appropriate symptomatic treatment. 3

Common Pitfalls

• Do not perform broad allergy panels or extensive laboratory investigations in typical acute urticaria; they are low-yield and can lead to false-positive results that complicate management. 3
• Do not attribute urticaria to food allergy without a clear temporal relationship and confirmatory testing, as this can lead to unnecessary dietary restrictions in a growing infant. 3, 1
• Recognize that most acute urticaria in infants is self-limiting and resolves spontaneously within days to weeks, even when no cause is identified. 1, 2