The aim of this study was to elucidate the relationships between the thickness, number, and frequency of scalp skin harvests and alopecia risk.
In a PubMed search, the search terms (scalp AND graft AND alopecia) were used, resulting in 148 papers. Among 21 abstracts, 11 full papers were reviewed, and 3 papers were ultimately analyzed.
The donor-site alopecia rate was significantly higher in patients who experienced hair growth on their grafts than in those who did not (odds ratio = 10.875, 95% confidence interval, 2.677–44.178; P < 0.001). The depth of the infundibulum can be estimated to be 451.8 μm at 5 years of age, 528.8 μm at 10 years, 605.8 μm at 15 years, and 682.8 μm at 20 years. Therefore, the limits of safe thickness for graft harvesting from the scalp are <18/1000 inches for 5-year olds, 21/1000 inches for 10-year olds, 24/1000 inches for 15-year olds, and 27/1000 inches for 20-year olds. The safe number of harvests (intersection of the alopecia and nonalopecia groups) was 2.7, and the safer number of harvests (limits of 2 standard deviations of the alopecia group) was 1.0. The safe time interval between harvests was 14.0 days, and the safer time interval between harvests was 15.6 days. The safe single minimal interval (SMI) between harvests was 12.7 days, and the safer SMI was 13.7 days.
Since the safe thickness for graft harvesting from scalps exceeds the thickness in usual practice, following the safer SMI between harvests (13.7 days) is expected to be more important for minimizing alopecia risk.