Because in so-called atopic dermatitis none of the skin lesions are primary in the sense that they develop de novo, no statement can be made about chronological sequence, either of the lesions themselves or of the disease itself. For example, if a patient scratches lightly, only reddish discoloration may result, but if scratching is more animated, erosions may come into being. If scratching is furious, ulcerations may be produced. If rubbing is done very lightly, there may be no morphologic manifestations of it. If, however, rubbing is to and fro vigorously for a long period of time, a plaque of lichen simplex chronicus may be formed. If only a discrete site is rubbed persistently with the ball of a finger, a papule or nodule of prurigo nodularis may be brought into being. If a discrete focus is both rubbed and scratched, an eroded or ulcerated papule of picker’s nodule may be brought forth.
Atopic dermatitis, because it results entirely from the effects of rubbing and scratching, may be reversed completely by cessation of external irritation. It may develop transiently if there are paroxysms of rubbing and scratching, and it may be sustained if there is nearly continuous rubbing and scratching.