Hives and angioedema are caused by inflammation in the skin. In some cases, hives and angioedema are triggered when certain cells (mast cells) release histamine and other chemicals into your bloodstream and skin.

Allergic reactions to medications or foods can cause acute hives or angioedema. Many allergens have been identified. Examples include:

Foods. Many foods can cause problems in sensitive people, but shellfish, fish, nuts, eggs, chocolate and milk are frequent offenders. Food additives, such as salicylates and sulfites, are other potential allergens.
Medications. Almost any medication may cause hives or angioedema; common culprits include penicillin, aspirin, ibuprofen (Advil, Motrin, others) and blood pressure medications.
Other allergens. Other substances that can cause hives and angioedema include direct contact with pollen, animal dander, latex and insect stings.
Additional triggers that may produce hives or angioedema include:

Physical factors. Environmental factors can result in the release of histamine with subsequent hives or angioedema in some people. Examples of these factors include heat, cold, sunlight, water, pressure on the skin, emotional stress and exercise.
Dermatographia. The name of this condition literally means "write on the skin." When pressure is applied to the skin or the skin is scratched, raised lines appear on those areas due to histamine-based angioedema that leads to swelling beneath the skin.
In addition to these triggers, hives and angioedema sometimes occur in response to your body's production of antibodies. This may occur because of blood transfusions; immune system disorders, such as lupus or cancer; certain thyroid disorders; infections, such as hepatitis; or even a cold.

Hereditary angioedema is an inherited form of angioedema and is related to low levels or abnormal functioning of certain blood proteins (C1 inhibitors). These inhibitors play a role in regulating how your immune system functions.

Signs and symptoms of hives include:

Raised, red or white welts (wheals, or swellings) of various sizes
A single welt or group of welts that can cover large areas of skin
Welts that resolve while new welts erupt, making it seem as if the condition "moves"
Burning or stinging in the affected area
Itching, which may be severe
Hives can be either acute or chronic. By definition, acute hives can last from less than a day to up to six weeks, whereas chronic hives last more than six weeks — sometimes occurring for months to years at a time.

Angioedema is similar to hives but occurs deeper in the skin. Signs and symptoms of angioedema include:

Large, thick, firm welts
Swelling of the skin
Blisters (bullae) in areas of severe swelling
Pain or warmth in the affected areas
Difficult breathing or swallowing, in severe cases
Angioedema often appears near your eyes or lips, but can also develop on your hands, feet, genitalia or inside your throat. Angioedema and hives can occur separately or at the same time.

Hereditary angioedema is a more serious — yet uncommon — condition that can cause sudden, severe and rapid swelling of your face, arms, legs, hands, feet, genitalia, digestive tract and airway. Signs and symptoms of hereditary angioedema include:

Sudden and severe swelling of the face, arms, legs, hands, feet, genitalia, digestive tract and airway
Abdominal cramping as a result of digestive tract swelling
Difficulty or obstructed breathing due to swelling of the airway
When to see a doctor
Mild hives and angioedema usually aren't life-threatening. You can usually treat mild cases at home.

See your doctor if the hives or angioedema doesn't respond to treatment or if your symptoms continue to appear for more than a couple of days. Seek emergency care if you:

Feel lightheaded
Have difficulty breathing
Feel your throat is swelling
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