Urticaria Pigmentosa
Urticaria Pigmentosa is a very uncommon rash which usually affects various parts of the body such as arms, neck, legs, and trunk of children including young adults. The rash consists of reddish-brown spots that turn into hives when they are rubbed hard or scratched. Sometimes the spots blisters.
Causes of Urticaria Pigmentosa
The spots in urticaria pigmentosa contain a large number of mast cells (infection-fighting cells that live in the skin). Mast cells make a substance called histamine, which causes hives, itching, and flushing. Experts do not know why people with urticaria pigmentosa have abnormal collections of mast cells in the skin. Most children who develop urticaria pigmentosa before the age of five will grow out of the condition by adolescence or early adulthood.