Dermatoglyphics

Dermographism:

• this is one of the physical urticarias. Seen in about 5% of the population, it is usually asymptomatic. It may however become symptomatic with features of discomfort or itching
• the reaction represents an exaggeration of the wheal response following scratching of the skin e.g. when towelling dry after a bath. The doctor can reproduce this condition by drawing a line on the skin of the back which results in linear wheals at the site of the 'line drawing'
• the patient who has dermographism may also have ordinary urticaria as well

White dermographism:

• seen in individuals with atopic dermatitis - in white dermographism firm stroking of the skin with a pointed instrument does not lead to the usual response characterized by a red line, flare, and wheal reaction - instead the initial red line is replaced, generally within a period of 10 seconds, by a white line without an associated wheal