Curriculum · ENT, Ophthalmology, and Dermatology
Urticaria
What it is
Urticaria is a vascular reaction of the skin characterized by wheals surrounded by a red halo, and it is caused by swelling in the upper dermis. Acute urticaria lasts less than 6 weeks. Chronic urticaria lasts more than 6 weeks, with daily or episodic wheals.
Causes and risk
Acute urticaria is idiopathic in half of cases. Upper respiratory tract infections make up 40%, drugs 9% and foods 1%. Chronic urticaria is spontaneous in 75%, meaning non-physical and non-vasculitic, and inducible in 25%; inducible forms include dermatographism, which is also called skin writing, and cold urticaria. The 75% spontaneous share is made up of idiopathic 45%, autoimmune 20%, pseudoallergic 5% and infection-related 5%. Acute hepatitis B infection can present as serum sickness, with fever, urticaria and arthralgia.
How it presents
The cardinal symptom is pruritus. Individual wheals usually last less than 24 hours, and a wheal that lasts longer than 24 hours should raise urticarial vasculitis. Angioedema may be associated, and headache, joint pain and gastrointestinal symptoms may go with it.