Is it hives or an allergy? How to tell the difference?

Urticaria (hives) is a mast cell-mediated disease characterized by the sudden onset of itchy, raised, and shifting urticaria plaques on the skin. Not all urticaria is an allergy.

Acute urticaria lasts less than 6 weeks; it may be associated with infection, certain medications, foods, or other triggers. It may recur after a specific food or medication, and targeted allergy assessment is meaningful if there is a recent association.

Chronic urticaria lasting longer than six weeks is classified as chronic spontaneous or chronic inducible urticaria. The majority of chronic spontaneous urticaria is not explained by a classic external allergen or food allergy. Therefore, arbitrary large food panels and unproven “intolerance tests” are not useful in most patients.

A typical urticaria plaque usually lasts less than 24 hours in the same area. If the same lesion persists for longer than 24 hours, is painful, or leaves bruising/pigmentation, different diagnoses such as urticarial vasculitis should be considered.

Patch tests are not routine tests for urticaria; they investigate contact allergies. Prick tests, on the other hand, investigate IgE-mediated acute allergies if there is a suitable clinical history. The choice of test should be made according to the mechanism of the disease.

Second-generation H1 antihistamines are the primary first-line treatment for urticaria. If control of chronic spontaneous urticaria is not achieved, dose optimization and further treatments, including omalizumab in appropriate patients, may be considered according to current guideline algorithms.