Hives Health Article

Definition

Hives is an allergic skin reaction causing localized redness, swelling, and itching.

Description

Hives is a reaction of the body's immune system that causes areas on the surface of the skin to swell, itch, and become reddened (wheals). These lesions are elevated, can be blanched with pressure applied from a finger, and are oval in shape. When the reaction is limited to small areas of the skin, it is called urticaria. Involvement of larger areas, such as whole sections of a limb, is called angioedema.

Causes

Hives is an allergic reaction. The body's immune system is normally responsible for protection from foreign invaders. When it becomes sensitized to normally harmless substances, the resulting reaction is called an allergy. An attack of hives is set off when such a substance, called an allergen, is ingested, inhaled, or otherwise contacted. It interacts with immune cells called mast cells, which reside in the skin, airways, and digestive system. When mast cells encounter an allergen, they release histamine and other chemicals, both locally and into the bloodstream. These chemicals cause blood vessels to become more porous, allowing fluid to accumulate in tissue and leading to the swollen and reddish appearance of hives. Some of the chemicals released sensitize pain-nerve endings, causing the affected area to become itchy (pruritic) and sensitive.

A wide variety of substances may cause hives in sensitive people, including food, drugs, insect or stings, and common household items. Common culprits include:

• nuts, especially peanuts, walnuts, and Brazil nuts
• fish, mollusks, and shellfish
• eggs
• wheat
• milk
• strawberries
• food additives and preservatives
• penicillin or other antibiotics
• flu vaccines
• tetanus toxoid vaccine

• gamma globulin
• bee, wasp, and hornet stings
• bites of mosquitoes, fleas, and scabies.
• dander from house pets
• new fragrances, laundry soaps, hand lotions, or articles of clothing
• certain plants, molds, chemicals, or dust particles

Symptoms

Urticaria is characterized by redness, swelling, and itching of small areas of the skin. These patches usually grow and recede in less than a day, but may recur in other locations, and complete resolution can take four to six weeks. Angioedema is characterized by more diffuse swelling. Swelling of the airways may cause wheezing and respiratory distress. In severe cases, airway obstruction may occur.