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Dr. Bertram Medical Hair Transplant
眉 髮 醫 學 移 植 中 心 ( 香 港 ) |
( 852 ) 3421-1138
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Follicular Units - The Building Blocks in Hair Transplant
The term Follicular Unit was first described by Dr. John Headington, a pathologist, in his 1984 paper “Transverse microscopic anatomy of the human scalp. Scalp hair follicles were observed to bind together underneath the skin, emerging from the scalp in clusters or groups of 1-5 hairs in each pore. Each grouping of hair is called a "Follicular Unit" or "FU". They are readily visible under 2X magnification.
In another word, all the hairs that emerge from a single orifice in the scalp is a Follicular Units. They are be further classified according to the number of hair contained.
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Occasionally some people may have up to 4 or 5 hairs per follicular unit ( 4-hair or 5-hair FU ). |
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Human has an unorganized pattern of groupings. Each individual has his/her own characteristic pattern of follicular units to give a unique appearance. One FU may contain :
- one to five terminal hair follicles
- one or more vellus hairs follicles
- sebaceous gland lobules
- insertion of the arrector pili muscle
Ratio of Follicular Units in Normal Chinese Scalp
| Ratio |
1 Hair FU |
2 Hair FU |
3 Hair FU |
4 Hair FU |
Hair-Graft Ratio |
| Men |
29% |
52% |
17% |
2% |
1.92 |
| Women |
33% |
49% |
16% |
2% |
1.87 |
What is a Graft?
The piece of hair-bearing tissue which is harvested and transplanted is called a GRAFT. A graft can be of different sizes and contains different number of hair or follicular units.
- A 4 mm biopsy contain 12-14 FUs
- A 2 mm mini-graft contain 3-4 FUs
- A 1 mm micrograft contain only 1 FU
Hair vs. Graft vs. Follicular Unit
As the latest Follicular Unit Transplant (FUT) uses only the smallest Follicular Unit, one graft can be considered the same as one Follicular Unit. Now please count the number of hairs in each of the following pictures.
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5 of the 1-Hair FU
Total - 5 grafts containing 5 hair |
4 of the 2-Hair FU
Total - 5 grafts containing 8 hair |
3 of the 3-Hair FU
Total - 3 grafts containing 15 hair |
Hair-Graft Ratio
Each individual will have a combination of 1-Hair FU, 2-Hair FU, 3-Hair FU... For a certain area the average number of hair per FU is known as Hair-Graft Ratio.
Hair-Graft Ratio = Total Number of Hair ÷ Total Number of FU
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Hair-Graft Ratio in Various Ethnic Groups
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Caucasian |
Africans |
Asians |
| Hair-Graft ratio |
2.3 |
2.3 |
1.8 |
Hair-Graft Ratio in Chinese Men & Women With Hair Loss
- There was on average 69 follicular units or 127 hair at the back of the head
- The number of hairs per follicular unit ( hair-graft ratio ) is 1.84
Hair-Graft Ratio in Chinese Men & Women Without Hair Loss
- There was on average 72 follicular units or 137 hair on the scalp
- About half of the follicular units contains 2 hair ( i.e. 2-hair FU )
- The number of hairs per follicular unit ( hair-graft ratio ) is thus 1.9
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Follicular Unit Density
For the same person FU density is highest in the midoccipital region ( back of head ), least in the supra-auricular area ( above the ears ). On average one square cm contains about 80 to 120 FUs, with individual and ethnical variation.
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Follicular Unit Density in Chinese Scalps
| Density (FU/sq.cm) |
Front |
Sides |
Back |
Average |
| Normal Men |
84 |
55 |
80 |
73 |
| Bald Men |
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68 |
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| Women |
87 |
54 |
72 |
72 |
| Bald Women |
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69 |
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Hair Density and Characters in Various Ethnic Groups
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Caucasian |
Africans |
Asians |
| Hair Density |
200 / sq.cm |
160 / sq.cm |
170 / sq.cm |
| FU Density |
100 / sq.cm |
60 / sq.cm |
90 / sq.cm |
| Hair-Graft ratio |
2.3 |
2.3 |
1.8 |
| Shaft Cross-Section |
Oval |
Elliptical |
Round |
| Shaft Diameter |
0.07 mm |
0.06 mm |
0.08 mm |
| Hair Shape |
Curly |
Wavy |
Straight |
| Length of Follicle |
4.5 mm |
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5.5 mm |
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In order to provide hair transplant service to patients from different ethnic groups, we have studies in depth the differences in their hair density and characters.
Exercise
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If you are still confused, may be we can do some exercise.
Count the number of FUs and the number of hairs within the red cycle.
Result:
1 hair FU = 2
2 hair FU = 11
3 hair FU = 3
Total FU or FU Density
= 2 + 11 + 3 = 16
Total Hair or Hair Density
= 2 + 22 + 9 = 33
Hair Graft Ratio
= 33 / 16 = 2
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Reference
Tsai RY, Lee SH, Chan HL. The distribution of follicular units in the Chinese scalp: implications for reconstruction of natural-appearing hairlines in Orientals. Dermatol Surg. 2002 Jun;28(6):500-3.
Unger et al. Hair Transplantation. 4th Edition
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