Page 123 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
So, having now defined the actual skin colour, how can we calculate the risk of injuring the epidermis with light energy.
1 00
90
80
70
60
Risk %
30
20
10
0
Ale xan dr it e Diode
IPL (averaged) Nd:YAG
Risk of epidermal skin damage
50
40
123456 Skin Colour
Figure 60 – Risk of epidermal skin damage for the four hair removal devices
To do this, we need to set up a suitable framework. We chose the maximum risk when the alexandrite laser is used on black skin – that is, 755nm on a 43% melanin concentration. This combination yields the highest possible melanin absorption coefficient (how ‘strongly’ the light is absorbed by the melanin).
Out of all of today’s devices and skin colours, this is the ‘riskiest’ possible option! So, using this as the ‘maximum’ risk, it is possible to calculate all the other scenarios, based on this worst-case scenario.
In essence, the values in the graphs above, show the ‘relative’ risk of epidermal melanin damage compared with the alexandrite/black skin scenario. (If anyone can come up with a better idea, please let us know.)
We have also assumed a typical wavelength range of 600 to 1200nm for the IPL treatments, which yields an averaged absorption coefficient similar to that of the diode laser (129 cm-1 for diodes and 122 cm-1 for IPLs).
________________________________________________________________________ 123 Chapter 3 Laser/IPL Hair Removal
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