By Dr. Cole, FUE Hair Transplant Pioneer

Hair Loss Density Study

Donor count
donor count
Hair loss donor count 1 square cm box

A thought began to brew in my mind last June at the ESHRS meeting in Brussels. Jean Devroye, MD introduced this thought to me. He noted that density studies done to date involved very irregular patterns. He suggested that his silicone sheets along with his regular patterns offered a solution to create a regular density. I agreed that some sort of standardization was needed.

As I contemplated his concerns further, I realized the obvious. Density studies without regular patterns create areas of high densities and areas of low densities. This was confirmed in my own patients where I average 45 grafts per square centimeter. Multiple measurements of postoperative density confirmed that in some areas I created 60 grafts per sq. cm, but in other areas, the density was 30, 40, or 50 grafts per sq. cm. In other words, one has to take an average density to derive an average density and my average density has been 45 grafts per square centimeter for some time.

The Ideal Yield

Recent studies suggest that the ideal yield at 10 months is with a density of 20 grafts per square centimeter. The yield at 20 grafts per square centimeter is greater than 90%. This is an ideal yield since typically 9 to 10% of all hairs on the scalp are in a resting phase. Yields begin to drop as densities exceed 20 grafts per square centimeter. At 30 grafts per square centimeter, they drop to 73% and this low yield continues at 40 grafts per square centimeter. This is alarming. These studies, however, raise some other very real concerns.

Imagine that you draw a 1 cm sq. box. Suppose you do your best to create a density of 10, 20, 30, 40, etc per sq cm. As the density increases the probability that isolated areas will have a higher density than other areas increases. How might isolated areas of increased density affect data? Well, I don’t think you need to venture far beyond the recent Korean study in Derm Surg. or the preceding three studies by Mayer, Keene, and Beehner. Perhaps, however, the results of these studies are skewed by the probabilities that isolated densities exceed the study parameters, while other areas within the same square cm. are far less.

My concern has been that a cumulative threshold of trauma triggers some sort of inflammatory response that impairs hair graft survival. Isolated areas of higher density might indeed be the source of such a cascade threshold of pathological sequelae. In other words, you might get great growth at 30 grafts per sq. cm, but potential pathological effects at 40 or 50 per sq. cm. This supposition is supported to some degree by Beehner who showed that in at least one instance higher densities produce ideal yields in some individuals. Might it be that if the yield at 40 grafts per sq cm is higher provided that the overall density is consistent?

Musings on Hair Density and Follicular Harvesting

Considering the many ways of counting follicular units or hairs is important when we discuss hair transplantation surgery. When a patient comes in for an evaluation for hair transplant surgery, the first thing we do is examine the donor area and write down what the follicular density in that area is, which can also be defined as the number of follicular units per unit area, which is usually about a square centimeter. The hair density, which is a number of hairs per square centimeter, is also highlighted.

T his information is beneficial as it gives is an approximate understanding of how much hair can be transferred to the recipient area, where the balding or thinning is taking place to the donor area. Tools such as the densitometer, Capillicare, Folliscope, and Trichograph can be used to measure the calculate density. However, these might provide fallacious results because hair counting is more difficult than it actually seems.

Look at the picture below and try to count the number of Follicular Units (FU’s). However, be sure that you count only the groups where the base of the scalp can be seen, where the hair is emerging from the scalp. You may have got 28 groups, and therefore it’s not too tough, is it?

Fig 1

4mm density 1

Next, you have to try and count the number of hairs. This is a little difficult. For this, you will have to classify the groups in categories of ones, twos, threes, and fours. To arrive at your hair density, you will have to add all these up. Then you have to divide the number of hairs that you get, by the number of Follicular units that you got and you will arrive at the CD or Calculated Density. This number if very important.

Fig 2

4mm density 2

What I’d like to say here is that it is very challenging to find an accurate hair count when you use optical machinery. Observing the hair in a single plane with the human eye will not prove to be as effective. You will find better results when you use an instrument that can be moved around and when you have the help of forceps to tease the hairs apart. This could mainly be because two hairs often sit adjacent to each other and can look like just one. If you go back to the photographs you will note that the second picture is the same as the first one, but have the number of hairs per FU written on it by hand. Some of them could easily fool you. For example, if you were to look at the big “two hair” unit, which is situated at a three o clock position, almost in the center, this is a three, and when you look at the “one hair”, which is a little to the right, it is a two.

This is indeed a problem when counting hairs, and unless there is no real-time ability that helps move the hairs or the viewers, correct answers will not be achieved. There is also another problem with CD or calculated density. While working with CIT, we have often noticed that the CD is higher than what is obtained when performing strip surgeries. If you are wondering why then let us tell you that the answer is relatively simple, you get what you see with strip surgery. If the particular strip has a higher number of one’s and two’s, you will have to work with that. There is no real way around it. The patient in the photograph has more one’s and two’s and hardly any fours or fives. The strip that has been taken from here is a low yield strip, in terms of the total number of hairs that are available.

With CIT, however, one can decide as harvesting is being done, which follicular units should be taken, and which can be left behind. If the patient has a high number of ones and two, then you have to cherry-pick. The threes and fours, are calling out to you to be harvested. What method do you think is the best to achieve the best results for coverage on the top of one’s head?

However, if the work is mostly being done on the hairline, and the one’s and two’s happened to be the preferred grafts, you have guessed it right. One can selectively harvest for those also. Therefore, what I am trying to convey is that CIT is convertible and has built-in flexibility, which only works for the patient’s interest. You can easily find the grafts that you want, and this is not just for follicular unit size. If the hair is fine, then more delicate hair will be needed for exact work on the edge of the hairline, where the transition zone has to be soft and feathered, but would coarser thick hair from the middle of one’s head be a better choice? Not at all. This is, in fact, the only area that any strip surgeon can harvest from, without making way for a scar that is grossly widened. This is one of the main reasons why, you will see many unnatural looking hairlines, even if the one’s and the two’s have been placed in the front appropriately, it is the caliber of the hair that is too large for the area. Just think about it, how will large pigmented, single hairs look, when they stick out from the hairline. Over here, the hair is supposed to be soft and feathered.

How can CIT be used to surpass this? Well, you should go low towards the nape of the neck. Find appropriate hair that is thin and feathery for the hairline. Everyone sees the hairline when they meet you and therefore it cannot afford to look out of place.

Soon we will publish interesting data, which discusses the changes in the density of the donor region in different areas.

Scalp Reduction And Donor Stretching Simulation

Is Laxity good? Is donor density decreased as a result of stretching?

scalp donor area streching

If you observe the video below, you may see that density on the simulated scalp reduces as it is stretched. The more the scalp is stretched, the more the hair density is reduced. This rule can be applied to strip hair transplant (FUT) harvesting method because density is calculated based on the number of follicular units over the total area under consideration. After a reduction, the crown hair growth direction tends to move lateral away from its natural forward growth angle. There is also a change in hair growth angles in the donor area following a strip harvest. Some “stretch-back” may help increase density on the scalp to a small degree. Tissue elasticity varies from patient to patient but reducing the scalp area inevitably reduces density. The total number of follicular units never increases after any reduction or harvesting and the overall appearance of the scalp and hair growth angles will be altered. For physicians, the only benefit of reducing the scalp is that the length of the surgical procedure is considerably reduced. For the patient, the benefit is the reduction in expenses for the procedure. The actual gain by the scalp reduction is usually partially or always lost after “stretch-back” occurs. This means the net gain is minimal. Density = the number of follicular units/surface area. Therefore, density decreases as the surface area increases as a result of stretching forces.

The Hair Density Study

Jean and I met recently to derive a study that creates a consistent density. We used his stencil to create a very regular pattern of recipient sites. Tree farmers among other mathematicians such as Ruifernandez and Francisco Jimenez, MD have shown that the highest densities are possible from triangular patterns as opposed to rectangular patterns. We used a triangular pattern in our study. We created a very regular pattern to study recipient site density and yield. In our study, however, we used body hair.

Jean and I suggest that future studies measuring density and yield should utilize his stencils in an effort to create a consistent and regular density.

The enclosed photos show a regular pattern for body hair grafts in a sagittal and coronal plane that includes single hair anagen body hairs. Such regular patterns avoid the potential for isolated areas of a much higher density. Once again, Jean and I suggest that future density studies should utilize such stencils to insure more useful data.

hair anagen body hairs


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