Abstract A 2‐year‐old, 2‐month‐old, 16.1 kg, female, neutered Border Collie on treatment for systemic histiocytosis, presented for crusting dermatitis predominantly affecting the limbs and abdomen. The patient had been diagnosed 7 weeks previously with systemic histiocytosis and was receiving prednisolone (0.93 mg/kg/day) and leflunomide (2.49 mg/kg/day). Cytology showed classic ‘railroad track’ cocci, confirming Dermatophilus congolensis from the affected lesions. Clinical remission was achieved after 8 weeks of topical therapy with a 3% chlorhexidine and Ophytrium mousse (Douxo S3 Pyo; CEVA Animal Health) and concurrent tapering of the systemic immunosuppression with no recurrence of the dermatophilosis‐associated crusts. Subsequent recurrence of cutaneous nodules consistent with flares of systemic histiocytosis were managed with short courses of prednisolone, with no recurrence of dermatophilosis.