Urticaria, also known as hives, is a skin reaction that causes itchy welts. The welts can be raised, red, purple, or skin-colored, and can vary in size, shape, and location on the body. Hives can be acute, lasting less than six weeks, or chronic, lasting more than six weeks. The condition can be caused by an allergic reaction to food, medicine, or other allergens, or by non-allergic triggers such as heat, cold, pressure, or stress. In some cases, the cause of hives cannot be identified, and the condition is called chronic idiopathic urticaria. Treatment for hives may include antihistamines, topical steroids, or other medications to reduce inflammation and relieve symptoms. In severe cases, temporary treatment with corticosteroids or immune modulators may be necessary. If you experience hives that do not improve after two days, are severe, or are accompanied by other symptoms such as swelling or a high fever, you should speak to a healthcare provider.