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Hives (known medically as urticaria) are smooth, raised, red, pink or white bumps of varying sizes that can appear suddenly anywhere on the body. They can cause discomfort and itching and can be made worse by scratching.

There are two kinds of hives:

• Allergic urticaria. Caused by the body’s overreaction to substances it encounters (allergic reaction).
  
  
• Nonallergic urticaria. Caused by factors other than an allergic reaction.
  
  

Individual hives usually last a few hours or a day and go away on their own. However, episodes can continue for varying periods of time. When hives occur deep in the skin, the condition is known as angioedema. There is no specific test to diagnose hives caused by allergic reactions or other factors. Diagnosis is based on:

• Close examination of the skin’s appearance and the eruptions themselves
  
  
• A detailed medical history, including exposure to potential allergens or irritants
  
  
• Ruling out disorders or diseases that may cause hives
  
  

The best treatment option for hives is to identify and remove the cause. Medications, such as antihistamines, may be recommended to relieve symptoms. However, treatment for hive-related conditions usually focuses on avoiding the situation or “trigger” that leads to an episode of hives. Though they vary among individuals, these may include:

• Allergens (e.g., foods, pollens, pet dander, insect stings)
• Autoimmune diseases
• Infections
• Irritants (e.g., cosmetics)
• Other factors (e.g., extremes in temperatures, sunlight, tight-fitting clothing)