Pityriasis lichenoides chronica (PLC) is a rare, chronic cutaneous disorder most commonly seen in children and young adults with a slight male predominance. The etiology of this disease is currently unknown. Two pathogenic mechanisms have been proposed: 1) PLC is an inflammatory response to an infection or antigenic trigger (temporal association to viral infection in some cases); or 2) PLC is a T-cell lymphoproliferative disorder (cases have demonstrated T-cell clonality). There is seasonal variation to this condition, with onset more often occurring in the fall or winter.

The disease is characterized by recurring crops of erythematous papules with central scale commonly seen on the trunk and extremities that can last from months to years. Its acute form is known as pityriasis lichenoides et varioliformis acuta (PLEVA). A rare and more severe ulcerative variant of PLC with systemic symptoms is febrile ulceronecrotic Mucha-Habermann disease. This condition is a dermatologic emergency.

The relationship of PLC and lymphomatoid papulosis and whether PLC is a lymphoproliferative condition with malignant potential remains controversial.