Pathogenesis of Chemical Leukoderma and Chemical‐Induced Vitiligo

Leukoderma/vitiligo is a serious pigmentary disorder that notably impairs the patient's quality of life. In particular, chemical leukoderma (CL)/vitiligo refers to acquired depigmentation of the skin induced by exposure to certain chemicals. In this review, the term “CL” is defined as the temporary, localized loss of pigmentation at the site of direct chemical exposure. When the causative chemical is removed, these skin patches undergo re‐pigmentation, indicating the restoration of melanocytes to their original condition. However, when the chemical‐induced skin depigmentation does not recover after the chemical is removed, or when de novo depigmented lesions emerge, it is classified as chemical‐induced vitiligo. This condition indicates that, even after chemical removal, the mature melanocytes cannot recover because of factors including, but not limited to, autoimmunity, stem cell depletion, and unknown factors. In this review, we summarized the latest pathological findings for each condition, focusing on rhododendrol, which is known to induce both phenotypes and cause an outbreak, which affected nearly 20,000 patients in Japan and other Asian countries.