[Woronoff rings in a mathematical model].

The width of a Woronoff ring is thought to be constant and independent of the diameter of the lesion. Clinical observations have allowed us to demonstrate that this is true only for lesions of a certain minimum size or greater. It is suggested that the paleness within the ring is caused by diffusion of a mediator from the psoriatic plaque into its environment. A mathematical model is formulated, and it is shown that clinical observations are consistent with the pathogenetic hypothesis. In addition, the mathematical model is used to derive some properties of the hypothetical mediator.