Estimating the number of lifetime follicular units: A survey and comments of experienced hair transplant surgeons

Background: Quantitative estimates of the yield of follicular units (FUs) containing likely "permanent" hair for hair transplanting have been only theoretically estimated. Objective: To clarify the number of likely permanent hair follicles in potential donor areas. Methods and Materials: Thirty-four highly experienced surgeons were surveyed and estimated the number of FUs containing "permanent" hair in hypothetical 30-year-old male patients with varying hair densities and destined to develop Type V or VI male pattern baldness (MPB). Results: Patients with average hair density and destined to develop Type V MPB were estimated to yield an average of 6,404 FUs, 4,963 FUs with below average density, and 7,904 FUs with above-average density. When Type VI MPB is anticipated, estimated mean harvest yields are 5,393 FUs with average density, 4,204 FUs with below-average density, and 6,661 FUs with above-average density. Conclusion: There are a finite number of FUs containing permanent hairs in any patient. The results of this survey provide a guideline that should be helpful in avoiding inappropriately aggressive goals such as creating overly dense or overly anterior frontal and temporal hairlines without regard for a cautious evaluation of the limitations of likely long-term donor/recipient area ratios. We present useful guideline numbers that can help physicians choose appropriate surgical goals.