Page 46 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 13 – Basal layer melanin heats up due to absorption of the light energy which leads to pain
Most of the pain felt by patient/clients in ALL photothermal treatments is caused by the epidermal melanin. This thin layer heats up after absorbing in some of the incoming light energy. If the melanin concentration is low (ST1 @ 5%, Figure 14) then the absorption is also low and the temperature rise is negligible.
Figure 14 - The temperature rise in the epidermal melanin, and hence the pain level, depends on the concentration of melanin in that layer – (a) where the concentration is only 5%,
However, if the melanin concentration is high (ST6 @ 40%, Figure 14) then the corresponding absorption of light is significantly greater than with the ST1 case, and, hence the temperature rise is much greater - leading to more pain for the same incident fluence.
The other, significant, consequence of the skin colour is that the remaining light energy which penetrates through the epidermis to reach the follicles, also depends on the skin colour since this effectively ‘steals’ some of that incoming light energy. Darker skins will allow less light through to the hair follicles. In a strange, counter-intuitive conclusion, this shows that darker skins should be treated with higher fluences, to compensate for this loss in the epidermis.
________________________________________________________________________ 46 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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