How Does an Allergic Reaction Cause Hives?

Hives are itchy, red, swollen welts on the skin that come and go, usually in a relatively short period of time. A single hive is usually a reaction to an outside irritant, such as an insect bite. Multiple hives are usually an allergic reaction to something internal, such as food, medication or infection. Stress or extreme cold or heat can also cause hives, as can exposure to sunlight or vigorous exercise.
But among the most common causes are allergies to food like shellfish, berries, eggs and nuts; or medications such as antibiotics, sulfa and aspirin.Hives can vary in size and usually appear on the throat, arms, legs and torso. About 20 percent of the population experience hives at one time or another during their lives.
Pollen and cat dander are also common culprits.

Hives occur when a chemical in the body, mainly histamine, is released from cells deep within the skin. For reasons not clear to physicians and allergy specialists, the body reacts to an irritant or stimuli. Sometimes the reaction is brief, lasting only a few minutes.

Ice or a cool compress may ease the discomfort. Sometimes, however, the hives may last for several days, requiring treatment with an antihistamine. Prolonged outbreaks should be evaluated by a physician, who may perform a series of tests to try and pinpoint the culprit. Try not scratch the affected area to avoid further irritation or infection. Wear loose comfortable clothing that will not put pressure on the area.
Once the allergen is determined, the best treatment is to avoid whatever caused the problem in the first place. You can also keep antihistamines on hand in the event of a future outbreak.