Scalp Biopsies for Alopecia.

BACKGROUND: Hair loss is one of the most common reasons patients seek dermatologic evaluation. Although clinical examination and trichoscopy establish the diagnosis in most cases, scalp biopsy remains essential when findings are inconclusive, when cicatricial alopecia is suspected, or when histopathologic documentation is required before systemic therapy. METHODS: This narrative review synthesizes evidence from PubMed/MEDLINE and Embase on the indications, biopsy site selection, sampling technique, specimen processing, and histopathologic interpretation of scalp biopsy in alopecia. RESULTS: Diagnostic yield depends on appropriate patient selection, trichoscopy-guided site selection, meticulous sampling, and optimal processing. A 4-mm punch oriented parallel to the hair shafts and extending into the subcutaneous fat, combined with horizontal and vertical sectioning (HoVert or Tyler technique), allows the most comprehensive assessment of follicular architecture. Histopathology reliably separates scarring from nonscarring alopecia and, in cicatricial forms, classifies disease by the predominant inflammatory infiltrate following the NAHRS scheme. Ancillary studies, including direct immunofluorescence, periodic acid-Schiff staining, elastic fiber stains, and microbiologic cultures, are applied selectively when clinically indicated. CONCLUSIONS: Integrating clinical, trichoscopic, and histopathologic findings improves diagnostic accuracy and guides therapeutic decisions. Close collaboration between the dermatologist and dermatopathologist maximizes the diagnostic value of scalp biopsy.