Hives, often due to toxins. See Hives.SkinEncyclopedia Entry for Urticaria :Urticaria pigmentosa. Urticaria pigmentosa occurs when there are too many inflammatory cells (mast cells) in the skin. Mast cells are immune system cells that help the body fight infections. Mast cells make and release histamine, which causes nearby tissues to become swollen and inflamed. Things that can trigger histamine release and skin symptoms include: Rubbing the skin Infections Exercise Drinking hot liquids, eating spicy food Sunlight, exposure to cold Drugs, such as aspirin or other NSAIDs, codeine, morphine, x-ray dye, some anesthesia drugs, alcohol Urticaria pigmentosa is most common in children. It can also occur in adults.The main symptom is brownish patches on the skin. These patches contain histamine. When histamine is triggered, the patches develop into hive-like bumps. Younger children may develop a blister that is filled with fluid if the bump is scratched. The face may also get red quickly. In severe cases, these symptoms may occur: Diarrhea Fainting (uncommon) Headache Rapid heartbeat.The health care provider will examine the skin. The provider may suspect urticarial pigmentosa when the skin patches are rubbed and raised bumps (hives) develop. This is called the Darier sign. Tests to check for this condition are: Skin biopsy to look for a higher number of mast cells Urine histamine Blood tests for blood cell counts and blood tryptase levels (tryptase is an enzyme found in mast cells).Antihistamine medicines can help relieve symptoms such as itching and flushing. Talk to your provider about which type of antihistamine to use. Corticosteroids applied on the skin and light therapy can also be used in some cases. Your provider may prescribe other kinds of medicine to treat symptoms of severe and unusual forms of urticaria pigmentosa.Urticaria pigmentosa goes away by puberty in about half of affected children. Symptoms usually get better in others as they grow into adulthood. In adults, urticaria pigmentosa can lead to systemic mastocytosis. This is a serious condition that can affect bones, the brain, nerves, and the digestive system.The main problems are discomfort from itching and concern about the appearance of the spots. Other problems such as diarrhea and fainting are rare. Bee stings may also cause a bad allergic reaction in people with urticaria pigmentosa. Ask your provider if you should carry an epinephrine kit to use if you get a bee sting.Call your provider if you notice symptoms of urticaria pigmentosa.Mastocytosis; Mastocytoma.Urticaria pigmentosa in the armpit Urticaria pigmentosa in the armpit Mastocytosis - diffuse cutaneous Mastocytosis - diffuse cutaneous Urticaria pigmentosa on the chest Urticaria pigmentosa on the chest Urticaria pigmentosa - close-up Urticaria pigmentosa - close-up.Habif TP. Urticaria, angioedema, and pruritus.