Urticaria pigmentosa is caused by excessive numbers of inflammatory cells (mast cells) in the skin. It is most often seen in children, but occurs 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 traumatized.

A large histamine release 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.

Urticaria pigmentosa is one of several forms of mastocytosis. Other forms include the solitary mastocytoma (a single lesion), and systemic mastocytosis (involvement in organs other than the skin).

• appearance of brownish lesions on skin
• welt or hive formation when lesions are rubbed or scratched
• blister formation over lesion when it is rubbed (younger child)
• facial flushing

• diarrhea
• fast heart rate
• headache
• fainting (syncope)

• urine histamine shows elevated levels of histamine
• skin biopsy confirms the presence of increased number of mast cells

Urticaria pigmentosa may resolve in 50% of affected children by puberty. Symptoms usually decrease in the other 50% 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 ask you to carry an EpiPen to be used in case of a bee sting.