Hives, also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. Hives may burn or sting. The patches of rash may appear on different body parts, with variable duration from minutes to days, and does not leave any long-lasting skin change. Fewer than 5% of cases last for more than six weeks. The condition frequently recurs.

Hives frequently occur following an infection or as a result of an allergic reaction such as to medication, insect bites, or food. Psychological stress, cold temperature, or vibration may also be a trigger. In half of cases the cause remains unknown. Risk factors include having conditions such as hay fever or asthma. Diagnosis is typically based on the appearance. Patch testing may be useful to determine the allergy.

Prevention is by avoiding whatever it is that causes the condition. Treatment is typically with antihistamines such as diphenhydramine and cetirizine. In severe cases, corticosteroids or leukotriene inhibitors may also be used. Keeping the environmental temperature cool is also useful. For cases that last more than six weeks immunosuppressants such as ciclosporin may be used.

About 20% of people are affected. Cases of short duration occur equally in males and females while cases of long duration are more common in females. Cases of short duration are more common among children while cases of long duration are more common among those who are middle aged. Hives have been described at least since the time of Hippocrates. The term urticaria is from the Latin urtica meaning "nettle".