The discoloration of the skin by metal that appears after rubbing on it with a blunt point: Black dermatographias are often the result of scratches, involving contact with other materials, and it can be confused with an allergic reaction, when in fact it is the act of being scratched that causes an image to appear.

These black dermatographias appear within minutes, in some cases accompanied by itching.

In normal situations, the swelling of black dermatographias will decrease without treatment within 15–30 minutes; however, in extreme cases, itchy red welts may last anywhere from a few hours to several days.