Terra firma-forme dermatosis (TFFD, Duncan’s dirty dermatosis) is a little-known skin disease with poorly understood etiology and pathogenesis. The true incidence and prevalence are unclear, and there are rather few publications on the disease. It is clinically characterized by skin hyperpigmentation with the formation of asymptomatic dirt-like plaques despite having good hygiene. Diagnosis is confirmed by lesion resolution after continuous applications of 70 % isopropyl alcohol. This is an ideal method for diagnosis and treatment, but lesions may recur.

Aim. To analyze a clinical case of terra firma-forme dermatosis (Duncan’s dirty dermatosis) in a child.

Results. Considering the disease rarity, the clinical case of terra firma-forme dermatosis (Duncan’s dirty dermatosis) in a 9-year-old boy with a comorbid allergic history is presented. The disease was possibly triggered by a complex effect (unhealthy diet, allergic anamnesis).

Conclusions. This presentation aims to capture attention to terra firma-forme dermatosis (Duncan’s dirty dermatosis). Inadequate awareness of this disease is the reason for worrying overdiagnosis. It is important to recognize this dermatosis to avoid irrational diagnostic and treatment procedures as well as to calm patients and family members. The paper is of interest to dermatovenereologists, pediatricians and general practitioners-family physicians.