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Hair Mapping

A Comparison of Caucasian and Korean Hair Density, Follicular Density, and Calculated Density; A Compelling Argument for Individual Follicular Group Harvesting

Numerous investigators have estimated donor area hair density and follicular density over the years. No published study to date has attempted to objectively quantify the total follicular density in the donor area. Numerous individuals have estimated follicular hair density in the Korean population, but no one has compared Korean densities with Caucasian densities using similar objective methods to measure these densities. The purpose of this study is to more accurately estimate hair density and follicular density in a finite surface area of the donor region and to compare these results in both Korean and Caucasian populations using the same method of measurement.
In addition to estimating the total number of follicular groups in the donor area, this study attempted to define the mean number of hairs per follicular group (calculated density) pre-operatively.1 We also evaluated the mean number of hairs per follicular group extracted by a method of individual follicular group harvesting (IFGH), commonly called follicular unit extraction or the FUE hair transplant technique, known as the Cole Isolation Technique (CIT®) and compared them to the donor area calculated densities that were determined pre-operatively.2,3 The purpose of this later comparison was to determine if there were specific advantages to this method of IFGH harvesting over strip-donor harvesting.
The results of this objective study showed that Korean follicular density and hair density is higher than previously reported in Asian patients. Caucasian hair density and follicular density are higher than in Korean people, but the difference is not as great as previously reported. Previous studies have shown that IFGH produces more hair per graft than does strip harvesting. This study re-confirms that IFGH does offer an advantage over traditional strip harvesting in that it produces more hair per follicular group and a higher percentage of follicular groups containing multiple hairs the distribution of grafts produced.

Objective

The donor area was divided into 14 regions of a specified size using a donor area template shown in Figure 1 (Device4Hair). There were 8 major regions and 6 minor regions as depicted in Figure 2. The major regions occupied the superior borders, while the minor regions occupied the inferior borders of the donor template. The intersection between the two borders lies along with the occipital notch along a line extending to a point 2 to 3 cm superior to the helix. The 8 major regions correspond to the current location where strip harvesting is traditionally performed. The eight major regions are numbered one through eight with numbers 1, 2, 3, and 4 on the right side of the scalp and regions 5, 6, 7, and 8 on the left side of the scalp.

Donor area template showing the size and location of 8 major regions and six minor regions.

Figure 1. Donor area template showing the size and location of 8 major regions and six minor regions.

The location of the 14 regions on the scalp with 8 major regions

Figure 2. The location of the 14 regions on the scalp with 8 major regions (number 1 – 8) superiorly and 6 minor regions (number 9 – 14) inferiorly.

Follicular density and hair density was measured using a 3.57 mm diameter circle, whose surface area is 10 square millimeters. This was done with a 30X handheld microscope (Radio Shack Cat No 63-851). The number of hairs and the number of follicular groups in 10 square millimeters within each region was noted and recorded in the Donor Area Analysis Sheet (Device4hair) shown in Figure 3. The mean follicular density in square centimeters within each circle was estimated by multiplying the number of follicular groups in the 10 square millimeter circles by 10. The total number of follicular groups within each region was estimated by multiplying the mean follicular density in each region by the surface area of each region. The number of hairs per square centimeter was determined by multiplying the total number of hairs in the 10 square millimeter circles by 10. The estimated total number of follicular groups in the donor area was defined by summing the estimated number of follicular groups in all 14 regions of the donor area. Calculated density has previously been defined as the number of hairs in each follicular group. 1 The calculated density was defined by dividing the total number of hairs in the 10 square millimeter circle by the total number of follicular groups in the 10 square millimeter circle. The calculated density estimates the mean number of hairs per follicular group. The mean calculated density of the entire donor region was obtained by taking the average of all the calculated densities in the 14 regions of the donor area.

Donor area analysis sheet

Figure 3. Donor area analysis sheet

<hrdata-mce-alt=”follicular-density” class=”system-pagebreak” title=”follicular density” />
  

The mean follicular density in each population of patients for all 14 regions was obtained by averaging the individual follicular densities of each region in both patient populations.

Grafts were obtained using a sharp punch method of IFGH extraction known as the Cole Isolation Technique, which is a proprietary system of FUE. Precisely varying the geometry of the punches used for extraction and precisely varying the method of the extraction minimized follicle transetion rates insured removal of intact follicular groups.

Upon removal of the follicular groups, the number of hairs in each group was determined under a Meji EMT dissecting microscope under 10X magnification. The number of hairs in each follicular group was noted. The total number of one, two, three, four, five, and six hair follicular groups were recorded for each patient. The relative frequency of each size group was totaled and the percentage of each size follicular group for each Korean patient. The overall frequency of each size follicular group was determined by averaging the number of each size follicular group in the Korean patient.

The total evaluated donor area measured 203 cm2. By multiplying the total donor area evaluated by the mean calculated density, we were able to quantify the total number of potential hairs available for transplantation in both the Korean and Caucasian populations.

PatientRegion 1Region 2Region 3Region 4Region 5Region 6Region 7Region 7Total Major

11575168016801680157518901680168013440
21225147014701470140016801470147011655
31750168016801680140021001680147013440
41400168016801470122516801470147012075
51750189016801680157518901890189014245
61225147016801470140016801470147011865
71400168018901680140016801890168013300
81400168014701680157516801470147012425
91225168016801470140018901470147012285
101575168016801470140016801680189013055
111225147014701260122516801470147011270
121400168014701680140016801680168012670
131575189016801680157518901890168013860
1487510501260105012251260105010508820
151575189018901680157518901890168014070
161575210021002100175021002100210015925
171575147014701260157516801470168012180
181575210016801680175018901680189014245
191750168018901680157521002100168014455
201225147012601470122514701470147011060
211400168018901680157516801680168013265
221400168018901890140014701680147012880
231750189021001890157518901890189014875
241750210018901680175021002310189015470
251400168016801260122514701680168012075
261400168014701680140014701470147012040
271575147014701470140014701680147012005
2810501260105012608751050126012609065
291400147016801470140014701470147011830
301575189018901680175021002100189014875
311750168014701470157521001680168013405
321750252025202520227525202520252019145
331400189016801470140016801680147012670
341575210016801680175018901680168014035
351225168016801470122514701470147011690
361400168016801470140016801680168012670
371400168016801470140014701470147012040
381225168014701680122514701470126011480
391750189016801470157516801680147013195
401575189018901470157518901680168013650
411225168016801680122516801470147012110
421750189018901890175018901890189014840
431750168018901680157521002100168014455
441400168016801680140014701470168012460
451225168014701260122514701470126011060
461750231025202100175023102100210016940
471750189018901680140018901890168014070
481575168016801470140016801680147012635
491575210021001890157516801680189014490
501750231018901890175018901890189015260
511225147016801470140016801470147011865
521400189018901680157516801680168013475
531575189014701470140016801470147012425
541575189016801470154718901890147013412
551750189016801680175018901890168014210
561225147014701470126012251470147011060
571575168016801680157518901680168013440
581575210016801680175018901680189014245
591750147016801680140016801680168013020
601225189018901470140014701470168012495
611575189016801680157516801890168013650
621925210023102100175021002100210016485
631400168014701470105014701470147011480
641400168016801470140016801470147012250

Average1,4901,7621,7101,6081,4821,7351,6871,63413,133

Table 1. The number of follicular groups for the Eight Major Regions in Caucasian Patients.

The Caucasian mean follicular densities for the six minor regions are noted in Table 2. In addition, the total number of follicular groups is noted for each patient in the minor regions along with the grand total of follicular groups for each patient. The mean number of follicular groups for each minor region is noted at the bottom of the table, as is the mean grand total for all 64 patients. The mean total for the six minor regions totaling 42 cm2 in Caucasian patients was 3,508 follicular groups. The mean total number of follicular groups in the 203 cm2 evaluated in the study group was 16,649 follicular groups.

PatientRegion 9Region 10Region 11Region 12Region 13Region 14Total MinorGrand Total

1700700700770770630427017710
2560560490420560560315014805
3560560490560490560322016660
4630560630630560560357015645
5560560490560490490315017395
6560490420420420490280014665
770070070063063067301009023390
8560490490560490490308015505
9560560490560490490315015435
10560630490560490420315016205
11420560490490490420287014140
12700630560630630560371016380
13700700490700700560385017710
14490490490420420420273011550
15770700560770560630399018060
16840840770840770770483020755
17560490490490490490301015190
18560630560630560630357017815
19700630560630560560364018095
20630560490560490490322014280
21490560560560630630343016695
22560560490630560490329016170
23700630560630560630371018585
24630630490630630560357019040
25630630630630560630371015785
26560560490560490490315015190
27490490490490420490287014875
28420280350280280350196011025
29490490490560560490308014910
30630560630560700490357018445
31630560490560560560336016765
32770840840910840770497024115
33560490490630560560329015960
34560560630490490490322017255
35490490560420490560301014700
36560560560560490560329015960
37560560560630560630350015540
38490490490490490490294014420
39630560490630630490343016625
40630630630700560560371017360
41560560490560490490315015260
42700700630700700700413018970
43700630560630560560364018095
44770560490700560560364016100
45560490420490420350273013790
46630630630700630630385020790
47490560560490490490308017150
48630490490560490560322015855
49700630630630630630385018340
50700560490630490490336018620
51560560490560560490322015085
52560560540560560490327016745
53560560490700560490336015785
54630560490630700700371017122
55630560630630560560357017780
56490490420560490420287013930
57700700700770770630427017710
58560630560630560630357017815
59560490630560630630350016520
60490490560490490490301015505
61630630560630560490350017150
62630630630630560630371020195
63630420560490420420294014420
64630560490560490490322015470

Average6025755455925556393,50816,649

Table 2. Number of Follicular Group Density for the Six Minor Regions in Caucasian Patients and the total number of follicular groups for all 14 regions.

The number of follicular groups for all eight Korean major regions are noted in Table 3. This table notes the total number of follicular groups in each region for all 30 Korean patients. The mean number of follicular groups in these 8 regions was 12,527 follicular groups. 

PatientRegion 1Region 2Region 3Region 4Region 5Region 6Region 7Region 8Total Major

11225210016801260122516801260168012110
21575189016801470122518901470189013090
31575189014701260157521001680168013230
41400168018901470122514701470126011865
51400189016801680140021001470126012880
61575189016801890140016801890147013475
71575189014701470140016801680168012845
81225147012601260105012601050147010045
91400189014701470157516801890147012845
101400189018901680175018901890147013860
111575168016801470140016801470147012425
121225105016801260122514701470126010640
131400147012601890122514701260168011655
141225147014701260122516801260147011060
151225189016801470140014701470168012285
161575210016801470157516802100189014070
171225168018901260122516801470147011900
181680168014701470189016801470126012600
191400189014701470122516801680126012075
201750189021001470157516801680147013615
21875147016801470105012601470147010745
221750189014701470175021001680147013580
2314001890168014701122516801470147022285
241225210018901680140018901680168013545
251225168014701680140014701680147012075
2687512601260105010501050126010508855
271400147016801470140018901680168012670
281575126014701260105014701050168010815
291400126012601050140016801260147010780
301225168016801470122514701470168011900

Average1386170816031449169116521526151212527

Table 3. Number of Follicular Groups for the 8 major regions in Korean patients and the mean total number of follicular groups in the 8 major regions for Korean patients.

The number of follicular groups in all six minor regions for the 30 Korean patients studied is noted in Table 4. This table includes the mean number of follicular groups for each of the six regions. The mean number of follicular groups in the six minor regions for the Korean study group was 3,191 follicular groups. The mean total number of follicular groups in all 14 regions for the Korean study groups was 15,718 follicular groups.

PatientRegion 9Region 10Region 11Region 12Region 13Region 13Total MinorGrand Total

1630490560700560630357015680
2630630630490560630357016660
3560490560560490490315016380
4560420490490490350280014665
5630490420490630420308015960
6560560630630560560350016975
7700560420630560490336016205
8980980840980700420490014945
9630630420630560420329016135
10560560560560420490315017010
11490490560490420490294015365
12490560420490630420301013650
13420420420630350420266014315
14490560490490630490315014210
15980560420840420490371015995
16560560210560560245269516765
17700490560700560630364015540
18630700630560560490357016170
19490420420560490490287014945
20560560560700490560343017045
21490490420490490490287013615
22560560420560490490308016660
23560560490560560490322025505
24560490560630560420322016765
25490560490490490560308015155
26420420350420350280224011095
27560560560490700560343016100
28560560490490490560315013965
29560420280490420350252013300
30560420420560490420287014770

Average586539490579523475319115718

Table 4. Number of Follicular Groups for the 6 minor regions in Korean Patients and the total number of follicular groups for all 14 regions.

Table 5 is a comparison of the mean follicular density of the eight major regions of Both Caucasians and Koreans. It also compares the mean number of follicular groups in each of the eight major regions of Caucasians and Koreans. The total number of follicular groups in the eight major regions for Koreans and Caucasians is also compared in this table.

PopulationRegion 1Region 2Region 3Region 4Region 5Region 6Region 7Region 8Total Major

Caucasian1,4901,7621,7101,6081,4821,7351,6871,63413,133
Korean1386170816031449169116521526151212527

Table 5. Comparison of the number of follicular groups in the eight major regions between Caucasian and Korean patients.

Table 6 is a comparison of the mean number of follicular groups in all six minor regions of Caucasians and Koreans. It also includes a comparison of the total follicular groups from all 14 regions and the total mean number of follicular groups in both Caucasians and Koreans.

Population

Region 9

Region 10

Region 11

Region 12

Region 13

Region 13

Total Minor

Grand Total

 
Caucasian6025755455925556393,50816,649
Korean586539490579523475319115718

Table 6. Comparison of the six minor regions mean number of follicular groups in Caucasian and Korean patients along with the total number of follicular groups in the minor region and in the entire 203 cm2 donor area.

Table 7 compares the mean follicular density in both Koreans and Caucasians. The mean follicular density was taken pre-operatively with a 10X microscope, which was previously described. The mean follicular density is an average of all 14 regions. Taking the mean from all 14 regions in a similar fashion derived the mean hair density. The mean calculated density was obtained by dividing the mean hair density by the mean follicular density.

Population

Mean Follicular Density in cm2

Hair Density in cm2

Mean Calculated Density in mm2

 

Caucasian

81.37193.072.37

Korean

74.81165.292.21

Table 7. Comparison of the mean follicular density, the mean hair density, and the mean calculated density in the 14 regions of the donor area pre-operatively in Caucasian and Korean patients.

Table 8 notes the distribution of follicular groups by size that was extracted from Korean patients by IFGH in the 30 Korean patients studied. The number of each size was calculated for each of the 30 Korean patients studied and the mean of each size is noted in Table 8.

 

1 hair

2 hair

3 hair

4 hair

5 hair

6 hair

Percent

2.1544.7147.025.570.550

Table 8. Mean percentage of follicular groups with respect to the number of hairs in each group in the 30 Korean patients studied

Discussion

Table 8. Mean percentage of follicular groups with respect to the number of hairs in each group in the 30 Korean patients studied

Table 8 notes the distribution of follicular groups by size that was extracted from Korean patients by IFGH in the 30 Korean patients studied. The number of each size was calculated for each of the 30 Korean patients studied and the mean of each size is noted in Table 8.

Most hair transplant procedures today involve the removal of donor tissue from the donor area with a scalpel. The typical donor area runs along the occipital scalp to a point superior to each ear. This line ranges from 28 to 30 centimeters generally. In our experience, the mean length was 28 centimeters but occasionally was up to 30 centimeters. Some physicians extend the line an additional centimeter anterior to the external auditory meatus bilaterally and some make the incision slightly more vertical laterally in an effort to increase the length of this line up to 34 centimeters.4 The typical strip harvest is between one to two centimeters in width.

In this study, the length of the donor area was 28 centimeters, which corresponds to the average length of a strip harvest. Generally speaking, the strip incision occurs within the 8 major zones depicted in this study. The eight major zones comprise 161 cm sq. It is felt that one can usually take ½ of this surface area and still have enough hair to cover the resulting strip scar. In other words, it is possible to remove 80.5 square centimeters and still have adequate coverage for the strip scar. Removal of a single strip 28 centimeters long and 1 cm wide removes 28 cm sq, while a 28 cm X 2cm wide strip removes 56 cm sq. The maximal width that can be removed and still leave 80.5 square centimeters above the incision is 2.875 cm. It may be possible to take as much as 119 square centimeters, which would leave 42 cm sq above the strip scar and 42 cm sq below the incision scar in the occipital and mastoid regions. This would correspond to a width of 4.2 cm. This would be possible provided there is adequate scalp laxity along with other ideal donor area conditions, and the strip scar remains covered. Unfortunately, the authors are not familiar with any such endeavor to date. Additional variables to consider with regard to strip scar exposure are the width of the scar, the color of the scar, degree of curl, and the caliber of the hair. The width of the strip scars is unpredictable. With more and more width excised, strip scars have a tendency to widen up to 0.5 cm in width though some physicians create scars in excess of 1 cm in width. Wider strip scars require a greater number of hairs to conceal them and tend to limit the total amount of donor tissue that can be excised. Coarse hair will generally cover much better than fine hair such that it is easier to conceal a strip scar provided the hair is coarse. Higher hair densities provide more hair mass and make it easier to conceal strip scars. Better hair characteristics and ideal circumstances may someday allow the physician to take up to 119 square centimeters of the donor area, while less favorable characteristics will make it less probable that such widths are possible. The total width of the excision affects the resulting width of the scar. Greater overall widths tend to produce wider scars.

Based on the mean follicular density and the mean calculated density in this study, the average 28 cm X 1 cm strip will produce the following number of follicular groups and hairs:

Caucasian 2278 FG5,400 Hairs
Asian 2,095 FG4,630 Hairs

The following discussion pertains to Caucasians although a similar argument could be generated for Asian patients. The maximal number of grafts than can be obtained in the average patient from 80.5 cm sq is 6,550 and the maximal number of hairs is 15,524. This probably represents the average maximal number of follicular groups and hairs possible from strip surgery. Graft counts, on the other hand, are generally higher than the total number of follicular groups. This occurs because physicians are rarely involved in the production of their grafts. Surgical technicians with variable levels of experience and training are generally the ones who dissect the strip into individual grafts. Based on numerous studies, experienced technicians produce a mean of 2.0 hairs per graft.3 With the removal of a strip, the total number of available hairs removed does not vary, but the number of grafts produced and the number of hairs transferred varies based on how the grafts are dissected by technicians, who have variable degrees of experience and training. If the average graft contains 2.0 hairs, but the average follicular group contains 2.37 hairs, then 0.37 hairs are removed from each graft. For example, if you have three follicular groups containing a 3, 2, and 3 hair respectively, then the average is 2.67 hairs per group. However if in the dissection process, you turn these three follicular groups into grafts containing 3, 2, 1, and 2 hair respectively, the average becomes 2.0 hairs per graft. This in fact is what happens in many strip surgeries as the percentage of one hair and two hair grafts far exceed the percentage of 1 and two hair groups in the donor area. The authors’ term this practice fractionation of the follicular group. Thus, if you assume that you can excise 80.5 cm, under acceptable donor circumstances (laxity, density, hair caliber, hair length, wave), then the average strip surgery clinic should produce 7762 hair grafts averaging 2.0 hairs per graft that total 15,524 hairs. Of course, waste from graft production in strip harvesting is generally not accounted for because physicians do not cut the grafts. Nor, do they generally moderate the efficiency of graft production. Therefore, many hairs may be lost due to waste.

The maximal number of grafts from strip surgery ranges between 4500 grafts to 8000 grafts in most strip harvesting clinics. In general, only those with ideal donor laxity and hair characteristics can achieve a total of 8000 grafts and it is worth pointing out that it is the scalps with greater laxity that form the widest strip scars. Using the mean follicular density of 81.37 and a length of 28 centimeters, the width of the donor area to produce 8000 intact follicular groups is 3.5 cm or 98 cm2 of a hair-bearing scalp. Suffice it to say that not many donor areas can tolerate such a voluminous amount of tissue excised especially if only a single scar is produced. Most donor areas probably tolerate a hair-bearing width between 2.875 cm and 3.0 cm of strip excision in the authors opinion.

Under exceedingly rare circumstances in a patient with average donor characteristics, the total maximum number of follicular groups possible from 119 cm sq is 9569 and the maximal number of hair is 22,679. This number far exceeds what most physicians have ever achieved in hair restoration surgery. This would leave only 42 cm2 of the donor area above the strip scar. The authors are unaware of any strip surgery that has achieved such a width of excision and this number of intact follicular groups.

Knowledge of individual patient characteristics such as their mean follicular density and their mean calculated density would allow the surgeon to gauge the efficiency of his procedure. For instance, if you produce fewer than 5400 total hairs from a strip of 28 cm2 in a patient with average follicular and calculated densities, then you have waste.

It is often stated among strip surgeons that you cannot produce more grafts from IFGH. It is generally accepted that you can remove up to 50% of a donor area and still have adequate coverage.5 If you consider that the average Caucasian donor area contains a mean follicular density of 16,641, one would on average be able to remove 8,321 follicular groups under the 50% rule of thumb. With IFGH you do not need to worry about scalp laxity and you do not need to worry about hiding a strip scar. Thus, you would almost always be able to achieve this number of grafts assuming that it is true that you can remove 50% of the donor density without producing thinness. The range of follicular densities in our 64 Caucasian patient study was 11,025 to 24,115 follicular groups. Accordingly, the range of potential follicular groups possible with IFGH is 5513 to 12,058 assuming you remove only 50% of the follicles. At the time of this publication, the authors are unaware of any patients who have had this many follicular groups extracted from their donor area, however. It is worth emphasizing that in IFGH the mean number of hairs per follicular group is 2.37, while it is 2.0 hairs per graft with strip surgery. Thus, with multiple strip procedures producing between 4500 to 8000 grafts, the average number of hairs possible is 9,000 to 16,000, while with IFGH the potential range of hairs on average is 13,066 to 28,577. The number of potential hairs with IFGH ardently exceeds the capacity of strip surgery and completely avoids the strip scar, the resulting donor area complications, and is independent of scalp laxity. Of course, IFGH averages 2.9 hairs per graft with the first 3000 grafts because it is possible to cherry-pick the grafts that contain the most hair. In other words, the first 3000 grafts harvested by IFGH will provide up to 8700 hairs on average, whereas, strip harvesting will provide an average of only 6000 hairs from 3000 grafts.  

Donor density measurements between observers in both Caucasian and Asian patient populations have varied over the years based on the investigator and the method of collecting the data. Part of the reason for such variability is a lack of consistency in experimental study design. Many physicians have resorted to an estimation based on phototrichograms.6,15 Such studies are potentially flawed as it is difficult to verify the size of the surface area and it is impossible to accurately count the hairs in each follicular group. Accurate hair counts depend on a verifiable study area and on hand counting each hair in a follicular group. Photographs will always undercount the number of hairs in the follicular groups, as it is impossible to separate hairs in a photograph. Photographs also tend to record a surface area that is larger than the planned area because the photograph is taken at an angle to the surface of the skin. Furthermore, the scalp is a curved surface along a three-dimensional plane. Photographs are a two-dimensional representation of a three-dimensional surface.

In 1984, Headington defined the follicular unit as the pilosebaceous unit as disclosed at the mid-dermal level.7 In 1995 Bernstein, et al defined the follicular unit as the cluster of hair as disclosed on the surface of the skin.8 In medicine, it is not possible to give two completely different anatomical structures the same name. Therefore, we have more correctly identified the cluster of hair seen on the surface of the skin as the follicular group and completely avoided the use of the term follicular unit (except when used by other investigators) as the follicular unit is a term referring a structure identified in a histology laboratory with hematoxylin and eosin staining. Furthermore, the follicular groups on the surface of the skin are at times composed of more than one follicular unit.9 Until this study, follicular density has lacked such an in-depth assessment. This study breaks the entire donor area into 14 finite zones of specific size using a donor area template and measures the hair density and follicular density in each region. It still estimates the total follicular density but the number of individual measurements in 14 specific regions and the use of a donor template provides a far more accurate estimate of hair density, follicular density, and the calculated density than has been previously reported. The comparison of Korean and Caucasian populations using a standardized format allows for a much more accurate comparison of Caucasian and Asian hair densities than has been previously reported. Of course, multiple measurements within each of the 14 regions would have yielded more accurate information, as would accurate counts within a larger reticule than 10 mm2. The authors have found, however, that larger reticules lead to greater experimental error as it is more likely to overcount or undercount as it becomes more difficult to recognize which follicular groups have already been counted and which follicular groups have not been counted as the reticule size increases. Therefore, the authors feel that 10 mm2 is the ideal surface area for counting follicular density and hair density with a handheld device. Hair densities will be undercounted with any handheld device, as it is not possible to separate hairs existing from a single follicular canal. Therefore, some three or four hair follicular groups will be respectively counted as two and three hair follicular groups. Hair counts done after excision of the graft will be more accurate as these are done under a 10 X Meji EMT microscope with better optics and with the ability to both separate surface hairs and identify follicular bulbs giving rise to their respective hairs.

Prior papers estimated the donor area on the assumption that the donor area consisted of ¼ of the total scalp.10 The total scalp was estimated to be 80 square inches with the donor area comprising 20 square inches.10 It was further estimated in Caucasian patients that the scalp has an average hair density of 2.0 hairs per sq. millimeter and that the follicular density averaged one per square millimeter by numerous observers.2,8 Of course, the follicular density was originally determined by Headington in his evaluation of punch biopsies taken from the crown of cadavers.7 The crown area has a higher follicular density than the cumulative donor area, based on the authors’ research, and it is well known that skin contracts when it is excised. The contraction artificially leads to a higher density and accounts for some of the errors in Headington’s conclusions. It was further estimated that the average scalp contains about 100,000 hairs.10 The average donor area with an average density of 2 hairs per square millimeter was assumed to contain 25,000 hairs or 12,500 follicular units based on this assumption.8 It was further estimated that as hair density increased, the total amount of movable hair increased proportionately. We have shown in this paper that the mean hair density is lower than the mean calculated density in both Caucasian and Korean patients. Furthermore, hair density by itself does not predict follicular density. One must know both the hair density and the calculated density to accurately note the follicular density.

In years past, the donor area often consisted of the major and minor regions that are noted in this study. More recently, strip harvesting below the occipital notch has become uncommon because a strip was taken from below the occipital notch often results in a wider strip scar. The area above the occipital notch totals 161 square centimeters or 25 square inches. The minor regions total 42 square centimeters or 6.5 square inches, while the total donor area comprises 203 square centimeters or 31. 5 square inches. Today strip harvesting is typically done in the sweet spot between the superior border of the minor regions and the superior border of the major regions. Strip harvesting in the inferior regions has fallen out of favor because this region is prone to wide strip scars. IFGH expands the donor area into the minor regions and offers a greater potential for grafts in both Caucasian and Korean patients.
The Caucasian patient has a mean follicular density in the major regions of 13,133 and the mean follicular density in the minor region is 3,508. The mean calculated density (hairs per follicular group) is 2.37. This corresponds to a mean total of 31,125 hairs in the major region and 8314 hairs in the minor regions or a total of 39,439 hairs in the donor region.

In the Korean patient, the mean follicular density in the major regions is 12,527 and the mean follicular density in the minor region is 3191. The mean calculated density (hairs per follicular group) is 2.21. This computes to a mean total of 27,685 hairs in the major region and 7,052 hairs in the minor regions or a total of 34, 737 hairs in the donor region. Prior studies in Korean patients indicated a potential between 10,375 and 15, 250 hairs based on patient age
The mean number of hairs per follicular group in Korean patients undergoing IFGH was shown to be much higher in this study than in previous studies. Pathomvanich found the distribution of follicular units in 30 Asian patients undergoing strip harvesting to be 23.65% 1 hair FU, 63.82% 2 hair FU, 12.52% 3 hair FU, and 0-1% 4 hair FU.11 The 30 Korean patients studied in this paper revealed a much lower percentage of 1 hair FU and a much higher percentage of 3 hair FU and 4 hair FU. In addition rare 5 hair FU was noted. Dr. Yoo found that the occipital region of young male Koreans with androgenic alopecia had a follicular distribution of 38.9% 1 hair, 37.4% 2 hair, and 23% 3 hair groups.6 A comparison of IFGH, Dr. Pathomvanich, and Dr. Yoo is depicted in Table 9 and Figure 4. In a previous study of Korean patients, Lee found the following distribution with IFGH: 1.5% 1hair, 37.2% 2 hair, 51.7% 3hair, 9.3% 4 hair, 0.4% 4 hair, and 0% 6 hair.3 Clearly, more data is needed to more accurately predict the overall mean with IFGH in Korean patients, but the data continues to confirm that IFGH offers more hair per graft than strip surgery in Asian patients.

 1 hair2 hair3 hair4 hair5 hair6 hair
IFGH2.1544.7147.025.570.550
Pathomvanich23.6563.8312.52100
Yoo38.937.423     0     0    0

Table 9. Comparison of the distribution of hair groupings as a percentage based on the number of hairs in each group in Asian patients pre-operatively, with strip surgery, and with IFGH.

Distribution of Follicular Group

Figure 4. Distribution of Follicular Group Size in Asian patients by three different investigators comparing the pre-operative donor area, strip harvesting, and IFGH.

Prior studies looking at the mean follicular density in Caucasians by Limmer noted 0.9/mm2, Bernstein and Rassman 1.0/mm2, and Cole 0.8/mm2.9,8,12 Prior literature in Korean patients suggested a range of 0.55 to 0.64 per mm2 depending on the age of the patient.13 In this study, the follicular density based on the total surface area of 203 square cm was 0.81 per mm2 in Caucasian and 0.75 per mm2 in Asian patients. This represents a much more similar follicular density than has been previously reported between Caucasian and Korean patients. Clearly data in this study far exceeds the estimates previously performed and shows that Koreans have far more hair in their donor regions than has been previously reported. Koreans are far better candidates for hair transplanted surgery than has been previously been reported based on this study.

Prior studies showed that Korean hair densities ranged from 0.83 to 1.22 hair per mm2.13 In this study, we found the mean hair density in Asian patients was 1.65 per mm2. Bernstein and Rassman suggested the mean hair density was 2.0 hair per mm2. In this study, the Caucasian hair density was 1.93 hairs per mm2.

The average number of hairs per graft with strip surgery in the Korean patient is 1.9 hairs.14 In IFGH the average number of hairs per graft is 2.53 in Korean patients. IFGH is particularly suited for the Korean patient as IFGH provides 0.62 more hairs per graft than does strip surgery. This results in better value to the Korean patient undergoing FUE and greater potential coverage with an equal number of grafts.

Previous studies have shown that the survival rates for IFGH are similar to those in strip harvesting and that transection rates with IFGH are generally less than in strip harvesting.3 Cumulatively, the data overwhelmingly supports IFGH as the method of choice in donor harvesting.

Conclusion

The authors have shown in numerous previous studies that the mean Caucasian follicular density is approximately 80 follicular groups per square centimeter. This study confirms the mean follicular density is similar to the authors’ previous findings. Using a similar protocol, this study showed that Korean hair density, follicular density, and calculated density are much higher than previously reported. In addition, this study shows that IFGH can produce a much higher percentage of grafts containing more than one hair in Korean patients. The results document that IFGH provides a much better solution for the Korean patient undergoing hair restoration surgery as the average IFGH graft contains 0.62 more hairs per graft than strip surgery provides in Korean patients.

Bibliography

  • Unger W, Cole J, Donor Harvesting, Hair Transplantation. W.P. Unger and R.M. Shapiro, eds. Marcel Dekker: New York, 2004; 307-308.
  • Rassman, WR, et al. Follicular unit extraction: minimally invasive surgery for hair transplantation. Dermatol Surg. 202: 28(8):720-27
  • Cole, JP, Status of individual follicular group harvesting, Hair Transplant Forum International, Jan/Feb 2009; 20-24.
  • Tykocinski, A, personal communication February 2009
  • Marritt E. The death of the density debate. Dermatol Surg 1999;25:654-660.
  • Yoo JH, Analysis of hair characteristics in Koreans using phototrichograms, Hair Transplantation. W.P. Unger and R.M. Shapiro, eds. Marcel Dekker: New York, 2004; 892-897.
  • Headington JT. Transverse microscopic anatomy of the human scalp. Arch Dermatol 1984:120:449-456.
  • Bernstein, RM, Rassman, WR, Szaniawski, W, Halperin, A, Follicular Transplantation, International Journal of Aesthetic and Restorative Surgery, Vol 3, 2, 1995, pp 119-132.
  • Cole JP. Mathematics of follicular transplantation, ISHRS, Washington, DC 1998.
  • Rassman WR, Carson S, Micrografting in Extensive Quantities, Dermatologic Surgery, Vol 21, 4, April 1995, pp 306-311.
  • Pathomvanich, D, Hair Replacement in Asians, Stough, D, Haber, B. (eds) pp 149-156.
  • Limmer BL. Personal communication 1998.
  • Korea Dermatology Society, 43.
  • Kuelachi, M. Review of the Asian hair surgery workshop. Hair Transplant Forum Intl. 17(3):94-95.
  • Neidel, F, Bretschneider, P, Measuring hair density and mass, Hair Transplantation. W.P.Unger and R.M. Shapiro, eds. Marcel Dekker: New York 2004; 876-886
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