How much hair can we transplant?
The scalp has a surface area of approximately 500 cm2 (50.000 mm2) and an average of 200 hairs per cm2 (80 - 100 F.U.´s). As a scalp with hair has one follicular unit per mm2 and each unit has an average of 2 hairs (for example an average of two hairs per mm2)there is a total of around 100.000 hairs. This number varies of course, from patient to patient and depending on the ethnic background. The best donor area is where there is hair that is permanently growing and which is genetically programmed to grow throughout the patient's life, these are the temporal and occipital regions. At the most, we can remove 50% of the hair present in the donor areas without causing these areas to appear thin or lacking in density. In theory, in the case of moderate male hair-loss patterns (type V or VI), 12.5% of the scalp is safely available to be transplanted. This is equal to 12.500 hairs or approximately 3.000 to 4.000 F.U.´s. The appearance of fullness has much to do with the mass of the hair. This is related to the number of hairs, the thickness of the individual hairs and locks of hair, texture, colour and whether it is straight or curly. On top of that, the contrast in colour between the scalp and the hair also significantly influences the optical illusion of fullness. Nowadays most experts agree that the average hair density in patients, who do not suffer from hair-loss, is 200 hairs per cm2 (the range goes from 130 to 280) and that only 50% of this number is required to achieve the appearance of normal density, that is 100 hairs per cm2 ( the range goes from 65 to 140). Put another way this is an average of 45 F.U.´s per cm2.  
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Paseo de la chopera, 66  Alcobendas - Madrid
912 939 427
Dr. José Lorenzo - Dra. Ximena Vila
Advanced Hair Transplant Clinic PIONEERS IN SPAIN Year 2003 FUE TECHNIQUE