Leukotrichia: A comprehensive review of follicular depigmentation.

Leukotrichia refers to whitening or depigmentation of hair resulting from reduced or absent melanin in the hair shaft. Although often considered a cosmetic finding, it may reflect underlying alterations in follicular melanocyte biology and therefore have diagnostic, prognostic, and therapeutic relevance. The clinical spectrum includes congenital and genetic disorders, including piebaldism, Waardenburg syndrome, tuberous sclerosis complex, and pigment dilution syndromes; autoimmune and inflammatory conditions, including vitiligo and follicular vitiligo, alopecia areata, and Vogt-Koyanagi-Harada disease; nevus- and melanoma-associated immune phenomena; drug-induced changes; and postinflammatory, traumatic, laser-associated, and idiopathic types. This narrative review, based on a structured literature search of biomedical databases, summarizes current evidence on terminology, follicular biology, mechanisms, etiologic spectrum, diagnostic approach, management, and prognosis of leukotrichia. Leukotrichia is best regarded as a final manifestation of diverse mechanisms, including congenital absence of melanocytes, immune-mediated melanocyte destruction, collapse of follicular immune privilege, melanocyte stem cell depletion, functional inhibition of melanogenesis, and structural injury to the follicular pigmentary unit. In vitiligo, hair depigmentation may indicate depletion of the follicular melanocyte reservoir and has been associated with a poorer response to medical and phototherapeutic interventions. In other settings, it may reflect stable developmental absence or structural injury with limited potential for repigmentation. Management is primarily cause-directed, and hair repigmentation should be evaluated separately from surrounding skin repigmentation in both clinical practice and research. Key priorities include standardization of terminology, development of specific outcome measures, independent reporting of hair and skin responses, and identification of predictive biomarkers for restoration of follicular pigmentation.