Presentation
The symptoms are thought to be caused by mast cells in the surface of the skin releasing histamines without the presence of antigens, due to the presence of a weak membrane surrounding the mast cells. The histamines released cause the skin to swell in the affected areas.
This weak membrane easily and rapidly breaks down under physical pressure causing an allergic-like reaction, in general a red wheal (welt) to appear on the skin. It can often be confused with an allergic reaction to the object causing a scratch, when in fact it is the act of being scratched that causes a wheal to appear. These wheals are a subset of urticaria (hives) that appear within minutes, in some cases accompanied with itching. The first outbreak of urticaria can lead to others on body parts not directly stimulated, scraped, or scratched. In a normal case, the swelling will reduce itself with no treatment within 15–30 minutes, but, in extreme cases, itchy red weals may last anywhere from a few hours to days.
Read more about this topic: Dermatographic Urticaria
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