Page 51 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Conclusion
Permanent hair removal by laser or IPL is not easy. But it is achievable, if the processes are fully understood and the correct parameters are chosen. Unfortunately, our 30+ years’ experience as laser researchers/trainers have revealed that many laser/IPL users do not really know how to achieve the best from their equipment. This is a serious issue, and not just for laser hair removal.
Thick and thin hair – how much light energy do they absorb?
How thick is a hair? Well, according to some research by physicist, Brian Ley (they do all the best research!!!), it ranges between 17 and 181 microns in diameter (see his results here). That is between 0.017 and 0.18 mm. (Note – other researchers have found a slightly different range of diameters).
So, that means that their cross-sectional areas [Area = 𝜋 x (radius)2] are between 0.0000023 and 0.00025 square centimetres!! Hairs are very small...
According to the data in Table 8 above, the number of hairs per square centimetre varies enormously across the body, from as low as 60 on the legs and thighs to around 880 on the cheeks.
30 70 10 52 2-4 500 70 30 12 16 3.5-4.5 65 80 20 16 12 2-4 80
Table 8 - Data from Richards & Merhag
If we multiply those numbers with the cross-sectional areas of the hairs, we can find how much hair (by area) there is in each square centimetre of skin:
________________________________________________________________________ 51 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022
Body Area
% Resting Hairs Telogen
% Growing Hair Anagen
Duration of Telogen (weeks)
Duration of Anagen (weeks)
Follicle Depth (mm)
Follicle Density (per cm2)
Chin
35
65
6
8-20
1-2.5
500
Upper Lip
Arm Pits
70
30
12
16
3.5-5
70
Pubic Area
Arms
Legs & Thighs
80
20
20
16
2-4.5
60
Breast
70
30
12
8-12
2-4
65