Test Your Knowledge

Hives (urticaria) are typically caused by the release of a chemical in the body. Known as histamine, this chemical causes blood plasma in the small blood vessels of the skin to leak out into the surrounding tissue. The plasma causes the red, swollen, itchy skin associated with hives. In addition, itching also results from the nerves being triggered by the blood vessel dilation associated with the histamine release.

The following factors may cause urticaria:

• Blood transfusions
  
  
• Cosmetic allergies or irritants, such as make-up, deodorant, perfume and lotion
  
  
• Drug allergies, reactions or side effects, such as to antibiotics, anti-inflammatory pills, aspirin, vaccinations, hormonal preparations, contraceptive pills, sedatives and diuretics
  
  
• Emotional factors, such as stress
  
  
• Environmental factors, such as exposure to sun or extreme cold/heat
  
  
• Excessive perspiration
  
  
• Fever, infections and infestations
  
  
• Food allergies, especially to eggs, shellfish, nuts, and milk
  
  
• Foods not related to allergies, such as tomatoes and fresh berries, as well as food additives and preservatives
  
  
• Indoor and outdoor allergies, such as to pollen, mold or animal dander
  
  
• Insect bites
  
  
• Pressure or friction on the skin
  
  
• Systemic and general diseases, such as hepatitis, lupus and mononucleosis

In addition, the likelihood of developing hives may be inherited. A patient with a family medical history of hives is more likely to develop hives themselves. Acute hives are more commonly seen in young people, and causes often include allergies to food and food additives and certain medications.

The trigger of chronic hives is often harder to diagnose. The cause of chronic hives is only identified in 10 to 20 percent of cases.

In approximately 50 percent of people with chronic idiopathic hives, the immune system is overactive and causes the release of histamine. In these people, exposure to an outside trigger is not needed. Their bodies simply attack normal tissues, resulting in hives. In other people, chronic urticaria may be related to thyroid disease or other hormonal problems.  Women with chronic hives often experience an increase in symptoms during premenstrual periods. In rare cases, the condition is associated with cancer.