Alternative names
Mastocytosis; Urticaria pigmentosa

Urticaria pigmentosa is a disease that produces skin lesions and intense itching. If the lesions are rubbed, hives may form on the site.

Causes, incidence, and risk factors

Urticaria pigmentosa is one of several forms of mastocytosis, which is caused by excessive numbers of inflammatory cells (mast cells) in the skin. Other forms include solitary mastocytoma (a single lesion) and systemic mastocytosis (involvement in organs other than the skin).

Urticaria pigmentosa is most often seen in children, but it can occur in adults as well.

Rubbing of a lesion produces a rapid wheal (a hive-like bump). Younger children may develop a fluid-filled blister over a lesion if it is scratched.

A large histamine release from these extra mast cells may cause flushing, headache, Diarrhea, a rapid heartbeat (tachycardia), and even fainting. This is uncommon with urticaria pigmentosa but may be seen in other forms of mastocytosis.


  • Appearance of brownish lesions on skin  
  • Welt or hive formation when lesions are rubbed or scratched  
  • Blister formation over lesion when it is rubbed  
  • Facial flushing

Severe form:

  • Diarrhea  
  • Fast heart rate  
  • headache  
  • Fainting (syncope)

Signs and tests

  • Urine histamine - shows elevated levels of histamine  
  • Skin biopsy - confirms the presence of increased number of mast cells

Antihistamines may relieve some of the histamine-induced symptoms such as itching and flushing. Discuss the choice of antihistamine with your child’s health care provider. With more severe and unusual forms of urticaria pigmentosa, systemic symptoms should be controlled with other medications.

Expectations (prognosis)

Urticaria pigmentosa goes away by puberty in about half of the affected children. Symptoms usually decrease in the remaining patients as they grow into adulthood.

In adults, urticaria pigmentosa may progress to the more serious systemic mastocytosis.


Discomfort from itching, and possible self-consciousness about the “spots,” are the primary complications. Other problems such as Diarrhea and fainting are rare.

Certain medications may trigger flares of urticaria pigmentosa. Discuss these with your doctor.

Bee stings may also cause severe allergic reactions in some patients with urticaria pigmentosa. Your doctor may advise you to carry an EpiPen to be used in case of a bee sting.

Calling your health care provider
Call for an appointment with your health care provider if your child has symptoms suggesting urticaria pigmentosa.

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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