Urticaria pigmentosa is an uncommon skin condition marked by a rash that usually affects the neck, arms, legs and trunk of children and young adults.

Urticaria Pigmentosa Rash on BackThe rash consists of reddish-brown spots that turn into hives when they are rubbed hard or scratched. Sometimes the spots will blister as well.

What causes urticaria pigmentosa?

The spots present contain a large number of mast (inflammatory) cells. Mast cells are immune cells that fight infection and live within the skin. They produce a substance called histamine. Histamine causes hives, itching, and flushing.

We do not currently know why people with urticaria pigmentosa have abnormal collections of mast cells in their skin. Experts believe there could be a genetic component to it. It is more likely to develop in children with allergies such as asthma or hay fever.

It is most common in infants, and most children who develop urticaria pigmentosa before the age of five will have resolution of the condition by adolescence or early adulthood.

When the skin condition starts after the age of five, the abnormal collections of mast cells will sometimes involve the internal organs and the disease does not always go away. A condition known as systemic mastocytosis can occur, which has symptoms such as low blood pressure, diarrhea, gastrointestinal bleeding and anaphylactic shock. These patients need blood tests and other studies to determine exactly what is going on.

Treating Urticaria Pigmentosa

Unfortunately for those suffering from this condition, there is no satisfactory treatment for urticaria pigmentosa.

Patients should avoid aspirin, codeine, opiates, procaine, alcohol and polymyxin B as well as hot baths and vigorous rubbing after bathing and showering. These can all release histamine which can cause itching, flushing and hives.

Bee or wasp stings can be particularly problematic for those with this skin condition, so your doctor may advise that you carry an EpiPen with you.

Antihistamines such as Benadryl can help control itching, hives, and flushing and PUVA therapy has been shown to be effective.