Chronic spontaneous urticaria (CSU)

Chronic spontaneous urticaria causes recurring hives and itching without an identifiable outside trigger, lasting more than six weeks. Mast cells sit at the center of the current understanding of this condition. When activated, they release histamine and other mediators that cause blood vessels to leak fluid into the skin, producing raised, itchy welts and sometimes the deeper swelling known as angioedema.

Research describes an autoimmune subset in which the body produces functional autoantibodies against IgE or its high-affinity receptor on mast cells, found in roughly 40 percent of patients studied, which helps explain resistance to standard antihistamine treatment in some cases. Other immune cells, including T cells and eosinophils, are also understood to help sustain the reaction. A precise general-population prevalence figure was not identified in this search, though the condition is understood to affect a meaningful minority of people who experience chronic hives.

Common signs

Recurring raised, itchy welts (hives or wheals) that can appear anywhere on the body, often coming and going within hours and shifting location. Some people also have deeper swelling (angioedema) of the lips, eyelids, hands, or feet. The intense itch can disturb sleep and daily life.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.