At the bottom of this posting, there are two examples of views of the donor area under a hand microscope (these can be purchased on Amazon.com). The microscopic view on the picture above averages about 2 hairs per follicular unit. This number is close to the average Caucasian’s density with a total hair count reflecting 100,000 hairs on the head. The picture below shows follicular units that contain far more than 2 hairs each (a very high donor density). Without calculating it but eyeballing it, it appear that the number of hairs exceed 3 hairs for each follicular group or more than 150,000 hairs on the head. Let’s assume that there are 3 hairs per follicular unit for the simplicity of the calculations that follow.
The average human has 50,000 follicular units on his hair baring scalp, averaging 2 hairs each which calculates to 100,000 hairs on the head. If you look at the Class 7 balding pattern patient, the remaining hair is the only hair that we can legitimately call permanent hair. This reflects 20% of the hair baring surface on the scalp (excluding neck hair) i.e. in a typical Caucasian male, 20% of the 100,000 hairs are permanent hairs for transplantation, which is 20,000 hairs or 10,000 permanent Follicular Units (grafts).
That means that if 10,000 grafts were taken out of the Class 7 patterned area, the area would be completely bald. Therefore the obvious question is how many grafts of these 10,000 permanent hair Folliclar Units (grafts) can we move. The answer depends on a series of factors, but let’s say safely that 60% can be moved safely, or 6,000 grafts with the FUE technique. If your hair has an average thickness or is more coarse, then number of harvestable grafts can be higher so that the remaining follicular units (grafts) will be enough to make the donor area look normal. If the hair is fine, however, the number of extractions that are safe will drop below the 6,000 Follicular Units (grafts) that can be safely harvested. When you or your surgeon push these numbers higher, you take a risk of donor area depletion which produces a see-through donor area (i.e. balding in the donor area). This is the reason I am writing this post, to give you, the reader, the power to understand the logic in the decisions on how to estimate the maximum number of grafts that you can move before risking a see-through donor area.
One reality is that most people don’t bald to a Class 7 pattern (only 7% of the male population), but might stop at a Class 6 pattern of balding, so if your surgeon and you decide that you are willing to extend the donor area to the Class 6 pattern of balding, then the number of permanent hairs will increase to 30,000 hairs and the number of harvestable grafts will be much higher with harvestable grafts possibly at 9,000 Follicular Units (or grafts) leaving 6,000 remaining follicular units to cover the donor area (the size of the Class 6 pattern of remaining hair). The decision to increase the projected size of the donor area has its risks because no one will know for sure that they will never develop a Class 7 pattern. The consequences of this decision is (1) the extra 3,000 transplanted grafts will not live and will die where ever they were placed if you develop a Class 7 pattern of balding, and (2) the harvested area will show with FUE area as white scars above the remaining donor area and these scars will be visible to everyone. So this decision should not be taken lightly and it must be discussed with your doctor at the time of the FUE, or you may regret the decision sometime in your future.
In the microscopic view of the patient on the right who has a very high donor density, the harvestable hairs in the Class 7 area may have doubled because the look of the donor area reflects not the number of hairs that were removed, but rather the number of hairs (or follicular groups or grafts) left behind. To calculate the safe harvestable number of grafts, the key is to leave behind approximately 4000 Follicular units. With an average Follicular Unit density of 3, the donor area contains 30,000 hairs or 15,000 Follicular Units (grafts) so that to leave behind 6000 grafts, this patient can safely harvest 9000 Follicular Units (15,000 – 9,000 = 6,000).
The use of strip surgery, on the other hand, always keeps the excised donor hair at the lower side of the Class 7 permanent zone, so that if your surgeon and you decide to take more grafts, other than a possible scar that may occur from the strip surgery, the risk of placing non-permanent hairs with the surgery is very low and the risk of seeing an area of harvested grafts with no hair will not occur. Of course, the risk here is potential scarring. The use of “Scalp Micropigmentation” solves the problem for either a see-through donor area or a scar. Here are examples of what can go wrong if things are not done right: https://newhair.com/baldingblog/collection-victim-photos-internet-harvested-depleted-donor-areas/