The triggering stimulus in dermographic urticaria or Urticaria factitia is the effect of shearing force on the skin brought about during rubbing, scratching or scrubbing (Ill. 3, 4).
Dermographic urticaria occurs in the general population at a rate of up to 5%, although different sources offer differing numbers. Patients with another form of urticaria tend to suffer from dermographic urticaria at even higher rates. Up to 50% of all patients with chronic urticaria present symptoms of dermographic urticaria at least part of the time. At particular risk are young adults between 20 and 30 years of age, with women slightly more likely to be affected. The duration of the illness ranges between 2 to 5 years, although such figures are of a purely statistical nature and are not applicable for individual patients.