Distribution of Human Hair in Follicular Units

The study, involving 50 patients, investigated the distribution of follicular units in the human occipital scalp to aid in planning follicular unit transplantation. It found that follicular unit density ranged from 65 to 85 units per square centimeter, with hair density between 124 and 200 hairs per square centimeter. A mathematical model was developed to estimate the donor size needed for transplantation, predicting the total number of follicular units and their composition in terms of 1-, 2-, and 3-hair units. The model suggests that for an average hair density of 160 hairs/cm², at least 11 cm² of donor scalp is required to harvest 800 follicular units. The study highlights the necessity of individual measurements due to variability among patients and acknowledges a potential graft loss of 10 to 30% during harvesting and dissection. The findings are specific to a Spanish population and may not be generalizable to other groups.