Follicular Unit Length Variation Across 14 Scalp Areas During Follicular Unit Excision: Analysis of 13,720 Grafts From 98 Patients

BACKGROUND: Follicular unit excision (FUE) has become predominant in hair restoration, yet precise recipient-site creation depends on accurate graft length. Follicular unit length (FUL) influences recipient-site depth, and mismatches may cause graft protrusion, dehydration, or folliculitis. The extent to which FUL varies predictably across donor regions within patients, enabling region-specific planning, remains poorly characterized. OBJECTIVE: The aim of this study was to characterize FUL variation across 14 donor scalp areas and establish a reference value in an admixed Brazilian population. MATERIALS AND METHODS: This cross-sectional observational study measured intraoperative FUL in 98 men undergoing first-time FUE at a single Brazilian center (May 2018-July 2019). In each of 14 scalp areas, 10 intact grafts per participant were measured in consensus by 2 surgeons. Participant-level means were computed per area and overall; their mean defined the universal follicular length (UFL). Regional differences were analyzed using a linear mixed-effects model. RESULTS: Among 13,720 grafts, UFL was 4.68 (SD, 0.13) mm. The mean FUL ranged from 4.43 mm (inferior temporal) to 4.89 mm (central superior occipital; difference, 0.46 mm; 10.4%). Age, weight, height, body mass index, and Norwood-Hamilton classification were not significantly associated with FUL. CONCLUSION: Follicular unit length varies significantly by donor scalp area. Region-informed planning and direct intraoperative measurement support precision-based FUE.