What causes chronic hives, and how are they treated?

Q. I have been diagnosed with systemic idiopathic urticaria. I have had recurrent hives and welts, sometimes covering 80% of my body for more than two months. I have seen an allergist and tried cutting certain foods from my diet. That hasn't helped either. Any suggestions?

A. Urticaria (hives) is often an incredibly frustrating condition. When the hives keep occurring for more than six weeks, as yours have, doctors call that chronic urticaria. The cause of chronic urticaria is found in a small percentage of patients.

When doctors cannot identify the underlying cause after a thorough diagnostic evaluation, we refer to the condition as idiopathic urticaria.

I suspect you and your doctors have considered the more common causes besides food and environmental allergens. These include:

• medications, including herbs, supplements, and over-the-counter drugs
• bug bites, such as scabies and bedbugs
• physical causes, such as pressure, cold or hot temperatures, and sun exposure
• exercise, as the skin gets warm and sweaty.

You probably have had a lot of blood tests already. Unfortunately, these tests usually don't point to a specific cause. Even a skin biopsy won't provide a specific answer in most cases. But it may be worthwhile to have a skin biopsy to exclude a rare condition called urticarial vasculitis.

Dermatologists now believe that many people given the diagnosis of idiopathic urticaria in the past actually had a form of an autoimmune disorder. For unknown reasons, a person's immune system may be triggered to react against their own skin.

Regarding treatment, people with persistent urticaria often need higher than usual doses of antihistamines. There are many to choose from.

Second-generation antihistamines are less sedating and doctors usually recommend one of these as first-line therapy. Examples include cetirizine (Zyrtec), desloratadine (Clarinex), fexofenadine (Allegra), levocetirizine (Xyzal), and loratadine (Alavert, Claritin).

The older first-generation antihistamines, such as diphenhydramine (Benadryl), can make you drowsy, so they are a good choice before bed. Other options are the anti-anxiety drug hydroxyzine (Atarax) and the antidepressant doxepin. Both have strong antihistamine action, but are also sedating, so they are best used at night.

Corticosteroids such as prednisone may be needed in severe cases. Because of side effects, doctors try to use the smallest dose for the shortest time.

The good news is that most often the hives do stop, but how long yours will persist cannot be predicted. Don't give up. Keep working with your doctors to find the best control of your hives until they stop.

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