Hives are raised, often itchy, red bumps (welts) on the surface of the skin. They are usually an allergic reaction to food or medicine. They can also appear without cause.
Urticaria; Wheals; Nettle rash; Angioedema; Quincke edema
When you have an allergic reaction to a substance, your body releases histamine and other chemicals into the blood. This causes itching, swelling, and other symptoms. Hives are a common reaction. Persons with other allergies, such as hay fever, often get hives.
When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema. Swelling can also occur around your hands, feet, and throat.
Many substances can trigger hives, including:
Hives may also develop as a result of:
Often, the cause of hives is not known.
Symptoms of hives may include any of the following:
Dermatographism is a type of hives. It is caused by pressure on the skin and results in immediate hives.
Your health care provider can tell if you have hives by looking at your skin.
If you have a history of an allergy, the diagnosis is even clearer.
Sometimes, a skin biopsy or blood tests are done to confirm that you had an allergic reaction, and to test for the substance that caused the allergic response.
Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:
If your reaction is severe, especially if the swelling involves your throat, you may need an emergency shot of epinephrine (adrenaline) or steroids. Hives in the throat can block your airway, making it difficult to breathe.
Hives may be uncomfortable, but they are usually harmless and disappear on their own. In most cases, the exact cause of hives cannot be identified.
When the condition lasts longer than 6 weeks, it is called chronic hives. Often, no cause can be found.
Call 911 or your local emergency number if you have:
Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care measures.
To help prevent hives:
Grattan CEH. Urticaria and angioedema. In: Bolognia JL, Jorizzo JL, Schaffer JV, eds. Dermatology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 18.
Saini SS. Urticaria and angioedema. In: Adkinson NF Jr, Bochner BS, Burks AW, et al, eds. In: Middleton's Allergy Principles and Practice. 8th ed. Philadelphia, PA: Elsevier Mosby; 2014:chap 36.