<unk>  is characterized by excessive amounts of mast cells in the skin. Red or brown spots are often seen on the skin, typically around the chest, forehead, and back. These mast cells, when irritated (e.g. by rubbing the skin, heat exposure), produce too much histamine, triggering an allergic reaction that leads to hives localized to the area of irritation, sometimes referred to as Darier's sign. Severe itching usually follows, and scratching the area only serves to further symptoms. Symptoms can be mild (flushing and hives that require no treatment), moderate (diarrhea, tachycardia, nausea/vomiting, headache, and fainting), or life-threatening (vascular collapse requiring emergency treatment and hospitalization).
Urticaria pigmentosa
Ichthyosis acquisita
Lamellar ichthyosis
Phytophotodermatitis
Ichthyosis bullosa of Siemens
Striate keratoderma
Dermatopathia pigmentosa reticularis
Ichthyosis vulgaris