Initial assessment
Diagnosis of urticaria should begin with identifying suggestive signs and symptoms. Urticaria is characterised by erythematous, pruritic wheals, usually with central pallor, varying in size and shape, which may coalesce and are migratory; each individual lesion resolves within thirty minutes to twenty-four hours, without ecchymoses or residual pigmentation. Angioedema presents as a sudden, pronounced swelling of the deep dermis/subcutaneous tissue, erythematous or skin-coloured, with paraesthesias, burning, tightness or even pain (more than itch), and a slower resolution, up to seventy-two hours.
Temporal classification
After clinical confirmation, determine duration: up to six weeks defines acute urticaria; more than six weeks defines chronic urticaria. The pattern may be daily or intermittent and recurrent.
Angioedema without wheals
In recurrent angioedema without wheals, consider exposure to angiotensin-converting enzyme inhibitors. Other drug classes, less frequent but possible, include angiotensin receptor blockers, DPP-4 inhibitors and neprilysin inhibitors. If symptoms remit after discontinuation of the angiotensin-converting enzyme inhibitor, this usually occurs within days (rarely up to six months). Persistence after stopping the drug should raise suspicion of hereditary or acquired C1-inhibitor deficiency; order complement C4 and C1 esterase inhibitor, consider genetic testing, and refer to Allergy/Immunology.
Systemic signs
In the presence of unexplained recurrent fever, arthralgia or malaise, consider autoinflammatory urticarial syndromes. In such cases, request a complete blood count, erythrocyte sedimentation rate and C-reactive protein to screen for systemic inflammation.
Urticarial vasculitis
If individual lesions persist on average for more than twenty-four hours, suspect urticarial vasculitis. Features supporting this include persistent (rather than evanescent) episodes, lesions that are tender/painful rather than predominantly pruritic, lesions leaving purpura or bruise-like discolouration, and associated symptoms such as fever, marked malaise, arthralgia, hypertension, proteinuria or haematuria. If suspected, a skin biopsy of lesions is indicated.
Inducible forms
Assess whether lesions are triggered by physical stimuli: cold, heat, pressure, sunlight, water (aquagenic), cholinergic (heat, exercise or sweating), contact urticaria and vibratory angioedema. Confirmation is by standardised provocation tests. If inducible, classify as chronic inducible urticaria; otherwise, classify as chronic spontaneous urticaria.
Differential diagnosis
In acute urticaria: atopic dermatitis, contact dermatitis, drug eruptions, insect bites, bullous pemphigoid, minor erythema multiforme, plant reactions, viral exanthems, Frey syndrome (auriculotemporal), and Sweet syndrome. In chronic urticaria: urticarial vasculitis, papular urticaria, mastocytosis, autoinflammatory syndromes, C1 esterase inhibitor deficiency, systemic lupus erythematosus, polymorphic eruption of pregnancy, hypereosinophilic syndrome, and anaphylaxis.
Investigation
In acute urticaria, as it is usually self-limited, additional testing is not required beyond a focused history to identify triggers. Exceptions: suspected food allergy in sensitised patients or drug hypersensitivity (especially non-steroidal anti-inflammatory drugs), in which case consider skin prick testing, specific immunoglobulin E to allergens and a supervised oral food challenge where appropriate.
Treatment — first line
First-line therapy is a second-generation H1 antihistamine taken regularly. First-generation antihistamines should not be used routinely due to central nervous system adverse effects. If control is insufficient, the dose of the second-generation antihistamine may be increased progressively up to four times the usual dose, with reassessment every two to four weeks. After control, taper gradually. For severe flares, consider short, intermittent courses of oral prednisolone (rescue dose ~0.5 mg/kg). Montelukast may be added in refractory cases, acknowledging limited evidence.
Special populations
In children, consider screening for and treating parasitic infections when indicated. Second-generation H1 antihistamines approved for ages two to eleven include cetirizine, levocetirizine, loratadine and rupatadine, with dosing adjusted by age and weight. During pregnancy and breastfeeding, when necessary and after risk–benefit assessment, prefer cetirizine or loratadine.
Second line
If, despite optimising first-line therapy, symptom control remains insufficient, consider second-line treatments such as omalizumab or ciclosporin in refractory patients, under specialist supervision.
