What Is Urticaria Pigmentosa?

Medically Reviewed by Jennifer Robinson, MD on May 11, 2023
Written by WebMD Editorial Contributors
4 min read

Urticaria pigmentosa is a rash that appears most often in children and young adults. It consists of reddish-brown lesions that may form hives or blisters when stroked. This reaction is called Darier's sign.

Urticaria pigmentosa is a type of mastocytosis. This is when the mast cells that are part of your immune system build up. Mastocytosis can occur in your skin, bones, intestines, or other organs. Urticaria pigmentosa is when the build-up of mast cells only happens in the skin.

Mast cells. Mast cells are part of your body's immune system. They are a type of white blood cell that is created in your bone marrow. Mast cells are found throughout your body, especially where your body interacts with the outside world. This includes your skin, lungs, and intestines. When your mast cells detect a germ, they release histamine to protect your body.

Genetic mutation. The abnormal build-up of mast cells that causes urticaria pigmentosa happens because of a mutation, or change, in a specific gene. This change usually happens in the womb, but it's not passed down from your parents. The reason for this mutation is not known. 

Indolent systemic mastocytosis. Urticaria pigmentosa is the most common form of mastocytosis in children. Mastocytosis is more likely to be chronic in adults and can progress to more severe forms. The most common form in adults is indolent systemic mastocytosis. Here, there is a build-up of mast cells in the skin as well as other areas, usually the bone marrow.‌

Some cases of mastocytosis can progress to even more severe forms of cancer. These include mast cell leukemia and mast cell sarcoma. In these forms of mastocytosis, there is a loss of organ function due to mast cells infiltrating the organs. This usually happens in the bone marrow, bones, gut, or liver. These forms of mastocytosis are aggressive and very rare. 

The most characteristic symptom of urticaria pigmentosa is a rash that appears primarily on the trunk, arms, and legs through Darier's sign. This sign occurs when the lesions are rubbed, which causes them to release histamine. They then become itchy, swollen, and will sometimes blister. In addition to Darier's sign, some people may experience the following symptoms:

  • Racing heartbeat
  • Diarrhea
  • Flushing (redness of the skin)
  • Wheezing
  • Fainting
  • Headache

More than 75% of urticaria pigmentosa cases start in children under the age of 10, but it can occur in older children and adults. In most cases, urticaria pigmentosa only causes skin problems and doesn't develop into the more severe types of mastocytosis.

The rash that occurs with urticaria pigmentosa is so specific that it can usually be diagnosed without any further tests. If your doctor thinks the urticaria pigmentosa may be part of wider systemic mastocytosis, you may need additional tests including:

  • Blood count, which will provide more information about the types and amounts of different cells in your blood
  • Serum tryptase, which tests for an enzyme that's released from mast cells
  • Bone density scan, which shows how strong and thick your bones are
  • A bone marrow test to see if your bone marrow is healthy and making cells

Most children will outgrow urticaria pigmentosa as they get older. There is no treatment to prevent new spots from forming. The spots may fade eventually but will usually last for years. 

As long as there is no systemic involvement, urticaria pigmentosa doesn't usually need treatment. The following treatments may help in certain cases:

You should also avoid anything that triggers reactions that make the symptoms worse. Some common triggering medicines include:

Some other triggers can include:  

  • Exercise
  • Rubbing the skin with towels
  • Hot baths
  • Hot drinks
  • Sunlight
  • Cold exposure
  • Spicy food

In very rare cases, urticaria pigmentosa can progress into systemic mastocytosis. People with mastocytosis are more likely to experience an anaphylactic shock. This is a type of life-threatening allergic reaction. Complications of systemic mastocytosis can also include:

  • Osteoporosis, which is when your bones become weak and soft
  • Cytopenia, which is when your body doesn't make as many cells as it should
  • Liver problems
  • Cancer (though rare, people can develop cancers involving mast cells)