Density Myth

Follicular unit density is generally highest in the midline of the donor area and decreases laterally. The majority of patients have density range from 1.5 hairs/unit to 3.0 hairs/unit with an average of 2.0 hairs /Follicular unit

The density of naturally occurring follicular units is 60 to 100 follicular units ( or 120 hairs to 300 hairs) per sq.cm Lower in this range in blacks and higher in this range in Caucasians.

"Cross Sectional Area." or diameter the range in terminal hair shaft diameter is approximately 60 micron to 140 micron.

It is interesting to note that compared to hair density, hair shaft diameter plays a much more significant role in the volume or "bulk" of the transplant.

Natural hair groupings in this case might be 20% 1's, 45% 2's, 30% 3's, and 5% 4's.

In our experience, the average donor density for all patients (both bald and non-bald) seeking a consultation for hair restoration surgery has an average donor density of 200 hairs/cm2. In general, for individuals with straight hair of average diameter, the donor density must be at least 100 hair/cm2 in order to adequately cover the donor area and not have it appear too thin. A density of 100 hair/cm2 is also the minimal density needed to hide an average donor scar. If a patient has wavy or thick hair the minimum density may be slightly less and in patients with very fine, straight hair the minimum density will be more.

A unit change in donor density away from the norm will produce a two-fold change in the availability of transplantable hair. For example, compared to the average person (with a donor density of 200 hairs/cm2), a balding individual with a donor density of 270hairs /cm2 (which is a 35% increase) will have 70% more hair available to transplant. Conversely, a person with a donor density of 130 hairs /cm2 will have 70% less transplantable hair, and may not be a candidate for surgery regardless of his Norwood classification. If he were to bald extensively, almost any type of hair restoration would leave him desperately short of hair and short on coverage in the donor area..

An average scalp is approximately 500 cm2. Since the normal, non-balding scalp has 100 follicular unit/cm2, and each unit contains on the average 2 hairs (yielding a density of 200 hairs/cm2), the average scalp would have 100,000 hairs in total. The permanent zone normally represents approximately 25% of this area, and half is available to be moved without the donor area appearing too thin. Thus, in theory, 12.5% of the scalp would be available for transplantation. This donor area would contain 12,500 hairs or 6,250 implants, averaging two hairs each. When a patient’s density is higher, a greater proportion of the donor hair can be used for the transplant.

Hence numbers are not as dismal as they appear. In a completel

y bald area, 17% of the patient’s original density offers a vast cosmetic improvement over having no hair, especially if the transplant is totally natural, and the patient has realistic expectations. But most importantly, the aesthetic impact of these absolute numbers can be improved upon with “artistic” adjustments in the “weighting” of the implants. In addition, if it can safely be assumed that the patient will not be extensively bald, then more hair can be committed to a more limited area. Great care must be taken so that excessive amounts of hair are not removed from the donor area to treat a limited area of recession, given the possibility that such a patient may need to reserve his donor hair to cover an almost certain evolving hair loss process over time.

The decision regarding moving hair reserves to meet patient’s goals must be a joint one between patient and doctor. The doctor has the obligation to fully inform the patient of the consequences of donor hair depletion when planning any reconstruction. We feel that the solution to increasing recipient density should be to perform a properly planned second procedure using follicular units and not to increase the size of the implants, since this will result in a density that is either equal to or greater than (due to compression) the

density of the donor area. This density will either be unnatural for a mature patient whose density in the front and top of his scalp should be less than in the donor area, or unrealistic if future hair loss should occur (and this level of density cannot be maintained). Conversely, splitting up the follicular units would not increase the density either. This would only produce groupings smaller than occur naturally and would run the risk of having poor growth and an appearance that was too thin.

n general (assuming straight, brown hair of average hair weight, and light skin), 50% of the hair in a given area may be lost before any appreciable change is noted. For the average person, with a density of 2.0, this would result in a density of 1 hair/mm2

hese numbers are not as dismal as they appear. In a completely bald area, 17% of the patient’s original density offers a vast cosmetic improvement over having no hair, especially if the transplant is totally natural, and the patient has realistic expectations. But most importantly, the aesthetic impact of these absolute numbers can be improved upon with “artistic” adjustments in the “weighting” of the implants. In addition, if it can safely be assumed that the patient will not be extensively bald, then more hair can be committed to a more limited area. Great care must be taken so that excessive amounts of hair are not removed from the donor area to treat a limited area of recession, given the possibility that such a patient may need to reserve his donor hair to cover an almost certain evolving hair loss process over time.

The decision regarding moving hair reserves to meet patients goals must be a joint one between patient and doctor. The doctor has the obligation to fully inform the patient of the consequences of donor hair depletion when planning any reconstruction.

We feel that the solution to increasing recipient density should be to perform a properly planned second procedure using follicular units and not to increase the size of the implants, since this will result in a density that is either equal to or greater than (due to compression) the density of the donor area. This density will either be unnatural for a mature patient whose density in the front and top of his scalp should be less than in the donor area, or unrealistic if future hair loss should occur (and this level of density cannot be maintained). Conversely, splitting up the follicular units would not increase the density either. This would only produce groupings smaller than occur naturally and would run the risk of having poor growth and an appearance that was too thin.

In a patient with a density of 2.4 hairs/mm2, the yield would be: 20% 1 hair implants 35% 2 hair implants 30% 3 hair implants 15% 4 hair implants

If we see with different perspective if the donor area has say 12500 hairs or 6000 Follicular units for the coverage of 375 cm2 area of the stage 7 Norwood baldness. If this hairs are equally distributed the density per cm2 would not be more than 16 /cm2. For say class 6 baldness the area may be 270 cm2 the equal distribution of 6000 follicular units will yield density of 22 FU / cm2. In other words if you are looking for density of 60 /cm2 in the entire area you would need 270 x 60 = 16200 FU ! But for good natural look it is important that one should have higher density in the front esp. in the hair line area (front 1 to3 cm) of at least 35 to 50 FU /cm2. This will obviously reduce the density in the area behind it because the available donor hair from the back are limited ( i.e. up to 6000 FU). More over covering the crown area with high density can consume a large number of FU and still will not give a dense cover because the whorl in the crown has centrifugal direction form the centre of the whorl and there is no shingling effect as in case of the front. More over crown is not making the framework of the face like the hair line so is cosmetically not as significant as the hair line and therefore priority should be given to the frontal cover rather than the crown cover. Our looks is judged majority of time from the front (Hair line) and very occasionally from the back side (crown).