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.