Do you know what is it? Or have you heard of Skin Writing?

Dermatographic urticaria (also known as dermographism, dermatographism or "skin writing") is a skin disorder seen in 4–5% of the population and is one of the most common types of urticaria, in which the skin becomes raised and inflamed when stroked or rubbed with a dull object

he 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, generally 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, accompanied by a sensation of burning, and itchiness. 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 wheals may last anywhere from a few hours to days.

(wikipedia)

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