Hives, also called urticaria, are raised areas of skin or welts. They usually form as part of an allergic reaction or sometimes from a virus and can range in size from less than an inch to as large as a dinner plate. Larger hives form when smaller patches merge together. These large patches are called plaques. Hives can appear anywhere on the body, including inside the genitals, mouth, throat, or ears. Deeper skin swelling, called angioedema, can accompany hives, and may occur on the eyelids and lips or hands and feet.
What causes hives?
Allergens are things you are allergic to. They cause cells lining blood vessels to release a chemical called histamine. This causes the water portion of blood to leak out, leading to the swelling and redness characteristic of hives. Common triggers for hives include:
- Insect bites
- Certain foods, including shellfish and nuts, especially peanuts
- Medications, such as aspirin and penicillin
- Contact with latex
- Physical stimuli such as rubbing of the skin or exposure to cold temperatures or to sunlight
In some cases, the cause of hives is not known. Doctors call this idiopathic hives.
What are other symptoms?
Symptoms of hives include:
- Single or groups of raised, red welts that may turn white (blanch) when pressed.
- Welts that have irregular edges. Hives are seldom perfectly round.
- Itching or burning. You may start itching in the area before hives appear.
- Welts disappear or reappear elsewhere on the body.
Hives usually disappear within a day. Chronic hives last longer than 6 weeks.
Hives could also be the first sign of a serious, body wide allergic reaction called anaphylaxis. If you see these warning symptoms, call 9-1-1:
- Difficulty breathing
- Chest pain or pressure
- Pounding heart or racing pulse
- Throat swelling, trouble talking, or hoarseness
- Sudden onset of wheezing
- Swelling of the face, neck, eyelids, lips, or tongue
- Severe abdominal cramping
- Hives that are widespread or spreading rapidly
- Fainting, dizziness, or confusion
What to do about hives?
Hives often don't need treatment. If you know what triggers hives, take steps to avoid the trigger. For itching:
- Apply a cool compress to the affected area.
- Take an over-the-counter antihistamine like diphenhydramine if it's OK with your doctor.
- Avoid hot showers.
- Wear loose-fitting clothes.
If the hives don't go away within a few hours or are severe, see your doctor.
Also call your doctor if you have a fever, or if you have just started a new prescription or over-the-counter medicine. Talk to your doctor before you take the next dose.
In addition to looking for an underlying cause, your doctor may prescribe stronger antihistamines or other medication to control the itching.
Created on 02/22/2011
Updated on 03/02/2011
- American Academy of Allergy, Asthma and Immunology. Tips to remember: allergic skin conditions.
- American Academy of Dermatology. Urticaria - hives.
- Asthma and Allergy Foundation of America. Chronic urticaria (hives).
- American Academy of Allergy, Asthma and Immunology. Allergic conditions: urticaria (hives)
- Duvic M. Urticaria, drug hypersensitivity rashes, nodules and tumors, and atrophic diseases. In: Goldman L, Aussielo D, eds. Goldman: Cecil Medicine, 23rd ed. Philadelphia, PA: Saunders Elsevier; 2007.