Factitious urticaria: red dermographism.

A type of reaction of the skin to superficial trauma is described which differs from ordinary dermographism. This is more easily evoked by rubbing and consists of an erythematous band in which diffuse wealing develops which can be palpated and more easily demonstrated by stretching the skin. Ordinary dermographism is excluded since a scratch as usually employed to demonstrate this produces erythema and not a well-defined raised weal. Forty patients who showed this reaction are described and it was also seen in three out of 100 normal subjects tested.