Causes of Hives, Urticaria and Angoedema

Urticaria develops when histamine is released into the small blood vessels (capillaries). The capillaries dilate which causes a welt, and fluid oozes into the surrounding tissue, causing swelling. Histamine also causes intense itching.

What Is Urticaria?

Urticaria, commonly known as hives, is a distressing disorder affecting up to 20 percent of the population at some point in their lives. The swelling that sometimes accompanies urticaria can lead to swelling of the face, hands and feet.

The rash of urticaria is usually bumpy, red and itchy. The bumps can be the size of mosquito bites to coin-size or larger, and can group together into irregular shapes. The rash will tend to come and go within a few hours, moving from one place on the body to another.

Categories of Urticaria:

Cases of urticaria can be acute, lasting less than 6 weeks, or chronic, lasting more than 6 weeks. The length of symptoms can often be a clue as to the cause of the symptoms. For example, the most common cause of acute urticaria in children is viral infections. Other common causes of acute symptoms include allergies (typically foods, medications, contact with animal dander and insect stings and bites), stress, and infections such as the common cold.

The most common cause of acute hives, particularly in children, is a viral infection. This may even be true if a child has not had any obvious recent illness. Acute hives can be related to other infections, such as strep throat, athlete’s foot and urinary tract infections.

Unlike acute urticaria, only about 5 to 10 percent of chronic urticaria are caused by allergies. Chronic cases are much more likely to be related to auto-immune causes than allergies. In the autoimmune form of urticaria, a person makes antibodies against a component of their mast cells, triggering the release of histamine and causing symptoms.

Other forms of chronic urticaria include the physical urticarias, in which the rash is triggered by stimuli such as heat, cold, sunlight, pressure and vibration. It is important to note that many forms of urticaria get worse with heat (such as from hot baths, exercise or wearing too much clothing) and pressure (such as around tight waistbands from clothing).

Lastly, some forms of urticaria are related to other diseases, such as other auto-immune diseases (such as lupus and rheumatoid arthritis), certain cancers, chronic infections such as viral hepatitis, and some hereditary forms.

Another common form of physically induced hives is called cholinergic urticaria. This produces hundreds of small, itchy bumps. These occur within 15 minutes of exercise or physical exertion and are usually gone before a doctor can examine them. This form of hives happens more often in young people.

How to Identify the Cause of Urticaria

In acute forms of urticaria a history of the events surrounding the outbreak is the most important information that can be obtained:

• Was there a specific food eaten or medication taken within minutes to hours before the symptoms started?

• Was the person stung or bitten by an insect shortly before the rash began?

• Had the person been ill from an infection, or had more stress in their life recently?

Unless there is information suggesting a specific cause, performing allergy testing is not usually needed for acute urticaria.

In chronic cases, a physician may check various blood and urine tests, and other procedures such as X-rays to look for other causes. If a physical urticaria is suspected, special tests to mimic the physical stimulus may be performed, such as placing an ice cube on the skin to cause a hive to form in people with cold urticaria. It is important to note that in most cases of chronic urticaria and angioedema, a specific cause is never found, and is termed “idiopathic.”

How Urticaria is Treated

The main treatment for urticaria is with antihistamines. These are usually given in oral forms, and may need to be given in large or frequent doses to control the symptoms. Short courses of corticosteroids may be needed, and rarely, if the symptoms are severe, epinephrine shots can be used for immediate, but temporary, relief.

If the cause of the urticaria is known or suspected, such as a food or medication, avoidance of this trigger may resolve the symptoms. In cases of chronic idiopathic urticaria, triggers such as acute infections of any kind (such as the common cold), stress, and use of non-steroidal anti-inflammatory medications (aspirin and ibuprofen, for example), may flare the symptoms.

In most cases of chronic urticaria and angioedema, symptoms last less than a few months to a few years. Some people may experience symptoms for many years, and those who do should be seen by an allergist for an appropriate testing and treatment.

Online Sources:

http://www.medicinenet.com/hives/article.htm

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001848/

http://allergies.about.com/od/skinallergies/a/urticaria.htm
http://allergies.about.com/od/faq/f/causeofhives.htm