Hives Rash Causes

Urticaria, or hives, as it is more commonly known, are formed when, in response to histamine, blood plasma leaks out of small vessels in the skin. Histamine is a chemical released from specialized cells along the skin's blood vessels. This is the body's defense mechanism and the histamine release can be caused by allergic reactions, chemicals in foods, insect stings, sunlight exposure or medicines. Sometimes it is impossible to find out why hives have formed.

There are several different types of hives, all of which can have different causes:

Acute Uticaria
These are hives lasting less than six weeks. The most common causes are foods, medicines or infections. Internal disease or insect bites may also be responsible.

The most common foods that cause hives, or uticaria, are nuts, chocolate, fish, tomatoes, eggs, fresh berries and milk. Fresh foods cause hives more often than cooked foods. Certain food additives and preservatives in packaged or canned foods may also be to blame.

Medicines that can cause hives, or uticaria, include aspirin and other non-steroidal anti-inflammatory medications such as ibuprofen, high blood pressure medications (ACE inhibitors), or pain killers such as codein.

Chronic Uticaria

These are hives lasting longer than 6 weeks. The cause of this type of hives is usually more difficult to identify than those causes of acute uticaria. For more than 87% of people with chronic uticaria, the cause is unknown.

Chronic uticaria can affect internal organs  such as the lungs, muscles and gastrointestinal tract. Symptoms include muscle soreness, shortness of breath, vomiting and diarrhea.

Physical Uticaria

These are hives that are caused by direct physical stimulation of the skin. For example - cold, heat, sun exposure, vibration, pressure, sweating and exercise. The hives usually occur right where the skin was stimulated and rarely appear elsewhere. Most of the hives appear within one hour after exposure.

Dermatographism

This type of hives rash forms after firmly stroking or scratching the skin. These hives can also occur along with other forms of uriticaria.