Dermatographic urticaria

Signs and symptoms

The condition produces a warm red wheal on the skin, often from scratching or contact with materials, which can be mistaken for an allergic reaction. Wheals appear within minutes and may be accompanied by itching. The first outbreak can trigger reactions on unstimulated body parts. In typical cases, swelling subsides without treatment in 6–30 minutes, but extreme cases may involve itchy red welts lasting hours to days, sometimes with a painful burning sensation that impacts quality of life.

Causes

Symptoms are thought to result from histamine released by mast cells on the skin's surface, causing swelling despite the absence of antigens. A weak mast cell membrane may break down under physical pressure, triggering an allergic-like reaction.

Triggers include stress, tight or abrasive clothing, watches, glasses, heat, cold, pressure on exposed skin, infection, diet, and air currents moving hair. The underlying cause is unknown; the condition may last years, subside, or be lifelong. It is not life-threatening or contagious and may occur in mastocytosis or mast cell activation syndrome.

Treatment

Treatment can include antihistamines, often combining H1 blockers or adding an H2 antagonist like cimetidine, to stop histamine from triggering the reaction. Daily 1000 mg of over-the-counter vitamin C helps break down and remove histamine. Cromoglycate, which stops mast cells from releasing histamine, works topically for rhinitis and asthma but is ineffective orally for chronic urticaria.