Hives
Hives (urticaria) are an allergic reaction of the skin. Hives are raised, red, itchy patches of skin (wheals or welts) that may appear and disappear at random. They range in size from less than a quarter-inch to an inch or more, and they may last as little as a few minutes or as long as a few days. Multiple hives may occur in response to a drug, food, or infection. A single hive commonly develops after an insect sting. Other possible causes include plants, inhaled allergens, stress, cosmetics, and exposure to heat, cold, or sunlight. Often a cause cannot be found.

Prevention
Avoid foods, medications, cosmetics, plants, insects, and animals that cause you to break out in hives. 
Reduce stress in your life. 

Home Treatment
Continue to avoid the substance that causes hives. 
Cool water compresses will help relieve itching. 
An oral antihistamine (Benadryl, Chlor-Trimeton) may help treat the hives and relieve itching. Once the hives have disappeared, decrease the dose of the
medication slowly over five to seven days.

When to Call a Health Professional ?
Call emergency services immediately if hives occur with the following signs of a severe allergic reaction, especially soon after taking a drug, eating a certain food, or being stung by an insect:

Lightheadedness or feeling like you may pass out. 
Swelling around the lips, tongue, or face that may interfere with breathing. 
Wheezing or difficulty breathing.
Call a health professional immediately If there is swelling of the lips, tongue, or
face that is not interfering with breathing. 
If many hives develop rapidly. 
If you commonly get hives, apply home treatment as your doctor has recommended.

Call a health professional: 
If hives persist for several days despite home treatment and avoiding suspected irritants.