Hives

In an allergic reaction, a person's immune system has been "primed", or "sensitized" to any one of a number of foods, medications, or other substances from the environment. In response to the substance, the immune cells release a chemical known as histamine. Histamine, in turn, acts on the capillaries in the skin, causing them to dilate and leak fluids. These fluids collect under the skin in welts which we recognize as hives.

Hives are characterized by itchy red welts and swelling of facial features. On occasion, hives can cause a life-threatening reaction that involves the whole body rather than just the skin. This is called anaphylaxis.

There are several known factors that cause histamines to be released, and hives to form. These include:

• allergy to medications or substances in the environment
• acute or chronic infections
• foods
• underlying systemic disease such as asthma, a condition that causes inflammation and obstruction of the airways in the lungs
• blood products given intravenously, or into the vein
• scratching
• heat or cold
• exposure to sunlight

Anaphylaxis is a medical emergency that can cause difficulty breathing and lead to death. It is important to call for emergency medical assistance immediately if anaphylaxis is suspected.

Antihistamine medications, such as diphenhydramine (i.e., Benadryl), cetirizine (i.e., Zyrtec) or loratadine (i.e., Alavert, Claritin), can be used to prevent hives. An individual should also avoid the substance that provoked the reaction if it is known. Epinephrine is used to treat severe reactions such as anaphylaxis.

A healthcare professional can diagnose hives after examining the affected person and listening to an account of the event.

Hives cause:

• discomfort
• skin irritation and breakdown
• skin infection

Hives are not contagious.

Hives can be treated in the following ways:

• identifying and removing the substance that provoked the outbreak
• using oral antihistamines such as diphenhydramine, cetirizine or loratadine
• using oral corticosteroids such as prednisone
• giving epinephrine for anaphylaxis

Both oral antihistamines and oral corticosteroids can have side effects, such as drowsiness, dry mouth, constipation and the inability to urinate. Antihistamines, especially the older ones such as diphenhydramine, can cause more severe reactions in the elderly.

Hives generally clear up without any long term problems. However, it is important to identify the cause and treat any underlying conditions.

If hives occur frequently, a healthcare professional should be consulted.