Pityriasis lichenoides Pityriasis lichenoides is the name given to an uncommon rash of unknown cause. Typical pityriasis lichenoides chronica Pityriasis lichenoides is probably a hypersensitivity reaction to a microorganism. No specific bacteria or virus has yet been identified however. It is not considered to be contagious.
Pityriasis lichenoides most often affects adolescents and young adults.
It is slightly more common in males. It is rare in infants and in old age. The spot flattens out over several weeks to leave a brown mark which fades over several months. Most often, the lesions occur on the trunk, thighs and the inner aspect of the upper arms. Pityriasis lichenoides rarely affects the face or scalp, but it can arise at any other site.