Page 57 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The reason is simply because darker hairs have a much higher concentration of melanin in them, compared with the skin (Table 24).
Clearly, as the skin colours darkens, the difference in temperature rise between the skin and the hair reduces. This strongly suggests that we must apply more cooling on darker coloured skins. But it also indicates that there is probably a limit on the skin colour we can safely treat, in terms of surface cooling.
So, the main point to take away from this is that we can happily cool the skin until the cows come home, and it should not affect the treatment outcomes at all – except it’ll make the treatments more comfortable and reduce the chances of unwanted skin damage.
CAVEAT – Obviously, do not induce frost bite or similar with too much skin cooling!! Depth of the germ cell bulges in hair follicles
Using this definition, the depths of the bulges can be seen in Table 12.
We will later calculate the ‘threshold’ (minimum) fluences required to effectively heat the germ cells in these bulges, at the depths, to ensure that they are all irreversibly denatured.
The depth of the germ cells bulge is critical in determining the required and threshold fluences needed to destroy follicles irreversibly.
The medical literature says that the bulge is between 1/3 and 1/2 of the way down a follicle, from the surface. We will take the 50% estimate – so that our threshold fluences should always be sufficient.
Figure 20 - Depth of germ/stem cell bulge
42
4.5 2.25
42
7 3.5
Table 12 – Depths of hair bulges across the body
Body Site
Follicle depth (mm) MAX
Max possible bulge depth (mm)
Chin
2.5
1.25
Upper Lip
Arm pits
5
2.5
Pubic area
Arms
4.5
2.25
Legs
Scalp
________________________________________________________________________ 57 Chapter 3 Laser/IPL Hair Removal
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