Background
The term dermographism (or dermatographism) literally means writing on the skin. Firm stroking of the skin produces an initial red line (capillary dilatation), followed by an axon-reflex flare with broadening erythema (arteriolar dilatation) and the formation of a linear wheal (transudation of fluid/edema); these events are collectively termed the triple response of Lewis.
An exaggerated response to this constitutional whealing tendency is seen in approximately 2-5% of the population and is referred to as dermographism. In a minority of people, it is accompanied by itching (symptomatic dermographism).
See the image below.
Dermographism urticaria. Courtesy of Professor Raimo Suhonen and DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/s/dermographism2.jpg).
Dermographism should be distinguished from other types of urticaria. See the following articles: