October 1, 2025, is World Urticaria Day.Urticaria is the medical word for hives — itchy red welts that appear on your skin. Acute urticaria happens in response to an allergy or some other source you can identify, like sun exposure. The welts usually go away with time or treatment. But chronic spontaneous urticaria, or CSU, are hives that occur suddenly, last for more than six weeks and, unlike acute urticaria, have no known cause.About 1% of people around the world get CSU. Most get it when they’re in their 20s to 40s, although you can get it at any age — even childhood. Women are twice as lik...

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