Safe Donor Area advances the fundamental principle of "donor dominance" established by Dr. Norman Orentreich. The objective in hair transplantation is to use only hairs that are destined to remain permanently in their original site. But how were such hairs to be found? To answer this question, Walter P. Unger, M.D. meticulously examined the scalps of 328 randomly chosen men with varying degrees of Male pattern baldness (MPB) who were over the age of 65 years. He looked for areas in which there were at least 8 persisting hairs per 4 mm diameter circle in the remaining hair-bearing fringe.
The hairs within these areas had obviously been the most immune to the causative factors involved in the development of MPB. While hair continues to be lost throughout the entire hair-bearing fringe of balding men during their lifetime, using the data that had been collected, Dr. Unger was able to outline a zone containing the hair follicles that were the most likely to be relatively permanent in approximately 80% of patients under 80 years of age. This quantitative model of a safe donor area has been and should continue to serve as the fundamental foundation in hair follicle harvesting for follicular unit transplantation (FUT), whether the grafts are being obtained via strip harvesting or via Follicular Unit Extraction (FUE). 
Harvesting hair follicles for transplantation from regions of the scalp lying outside the borders of the safe donor area poses two increased risks: 1) only temporary survival of the transplanted follicles, and 2) subsequent donor scar exposure if the follicles have been removed from a region of eventual substantial or total hair loss. As implied above, the latter is true regardless of whether the donor tissue has been obtained by strip harvesting or FUE. Of course, the safe donor area represents a generality that cannot be reliably depended upon for any particular individual. For example, the likelihood of the long-term survival of hair outside of the "safe donor area" will be greater in an older patient than in a younger one - in whom ultimate fringe width and fringe hair density is less predictable than in an older man. What can be depended on, however, is that the closer the donor sites approach the advancing edges of MPB (the upper and lower borders of the fringe) the more likely the previously noted risks will become a reality.