Urticaria and Hives - Causes

Introduction Causes Symptoms Treatments

Hives and angioedema form when, in response to histamine, blood plasma leaks out of small blood vessels in the skin. Histamine is a chemical released from specialized cells along the skin's blood vessels.

Allergic reactions, chemicals in foods, insect stings, sunlight exposure, or medicines can all cause histamine release. Sometimes it's impossible to find out exactly why hives have formed.

Acute urticaria and/or angiodema

Hives or swelling lasting less than six weeks.

  • The most common causes are foods, medicines, latex, or infections. Insect bites and internal disease may also be responsible.
  • The most common foods that cause hives are nuts, chocolate, fish, tomatoes, eggs, fresh berries, soy, wheat, and milk.
  • Fresh foods cause hives more often than cooked foods. Certain food additives and preservatives may also be to blame.
  • Medicines that can cause hives and angioedema include aspirin and other nonsteroidal anti-inflammatory medications (NSAIDs, such as ibuprofen), high blood pressure medications (ACE inhibitors), or painkillers such as codeine.

Chronic urticaria and/or angioedema

Hives or swelling lasting more than six weeks.

  • The cause of this type of hives is usually more difficult to identify than those causing acute urticaria and/or angioedema. The causes can be similar to those of acute urticaria but can also include autoimmunity, chronic infections, hormonal disorders, and malignancy.

Physical urticaria

Hives caused by direct physical stimulation of the skin --

  • For example, cold, heat, sun exposure, vibration, pressure, sweating, and exercise.
  • The hives usually occur right where the skin was stimulated and rarely appear anywhere else. Most of the hives appear within one hour after exposure.


Hives that form after firmly stroking or scratching the skin. These hives can also occur along with other forms of urticaria.

Hereditary angioedema

This is painful swelling of tissue. It is passed on through families.