How can I differentiate between acute and chronic urticaria in my patients?

To differentiate between acute and chronic urticaria in patients, focus primarily on the duration and pattern of symptoms. Acute urticaria is defined by the presence of wheals and/or angioedema lasting less than 6 weeks, often with identifiable triggers such as infections, drugs, or allergens, and typically resolves spontaneously or with short-term treatment ¹. In contrast, chronic urticaria is characterized by recurrent or persistent wheals and/or angioedema lasting for 6 weeks or more, often without an identifiable external cause, and may require longer-term management ¹.

Clinical history is key: For acute urticaria, patients usually report a sudden onset of symptoms, often linked to a recent exposure to a trigger, with episodes lasting hours to days but resolving within 6 weeks ¹. Chronic urticaria patients experience daily or almost daily symptoms for more than 6 weeks, frequently without clear triggers, and symptoms may wax and wane over months or years ¹.

Use of symptom diaries and validated tools such as the Urticaria Activity Score (UAS7) can help assess the frequency, duration, and severity of episodes, aiding differentiation and monitoring. A UAS7 score over 28 per week indicates severe disease, often seen in chronic urticaria, whereas acute urticaria tends to have lower scores and shorter duration ¹.

Physical examination and history should also assess for associated features: Acute urticaria may be accompanied by systemic allergic reactions or anaphylaxis, especially if related to drug or food allergy, which typically have rapid onset after exposure ¹,². Chronic urticaria is less commonly associated with systemic symptoms but may coexist with autoimmune or inducible triggers ¹.

Investigations are generally not required for acute urticaria unless severe or atypical, but for chronic urticaria, consider targeted investigations to exclude underlying causes or triggers, including autoimmune screening and assessment for inducible urticarias ¹.

In summary, the key differentiator is symptom duration: less than 6 weeks for acute urticaria and 6 weeks or more for chronic urticaria, supported by clinical history, symptom pattern, and use of assessment tools.