27-year-old man presented with pigmented macules on the right sole, which showed a parallel-ridge pattern on dermatoscopy. His work for a chemical company involved handling para-phenylenediamine. Histological examination of a biopsy from a lesion did not find any proliferation of atypical melanocytes. Shaving the cornified layer of the lesions with a surgical knife resulted in the disappearance of macules. We speculate that para-phenylenediamine on the sole of the patient's work boot might have become blotted to the cornified layer of the cutis. This report adds a new occupation-related differential diagnosis for skin diseases showing a parallel-ridge pattern on dermatoscopy.