Overharvesting of the Donor Area -

How many hair follicle units are there in the donor area?

The donor area refers to the area in the back of the scalp that hair follicles are taken from during a hair transplant.

The density of the typical donor area is around 80-120 follicular units per square centimetre. Measuring length x width, it's easy to determine that a typical person has about 20,000-25,000 follicular units covering the back of the scalp. 

How many follicles can we take?

But if we were to take all 20,000 follicular units, the patients would be bald and the whole point of doing the hair transplant would be lost. 

In general, we can harvest , we can usually extract 15-20 % of the grafts in an area without any concern for the area looking thin or "bald". With a 1 mm FUE punch we can extract up to 20 follicular units per sq cm and with a 0.75 mm punch we can extract up to 25 follicular units per sq cm. I rely on a careful measurements to guide surgery. For most donor areas, this works out to be 5000-7000 follicular units. Sometimes more can be harvested, sometimes not. 

The term for excessive harvesting of hairs in the donor area such that the area starts to look abnormal and cosmetically unacceptable is 'overharvesting'