Page 181 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
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).
The graphs (Figure 101) show that the long-pulsed Nd:YAG is, by far, the safest option when considering epidermal damage, for all skin colours. The maximum risk, with this wavelength (1064nm) is only 30% (compared with 100% for the Alex/black skin combo), meaning that the Alexandrite laser is more than three times more likely to induce unwanted damage than the Nd:YAG laser.
If we assume that an ‘acceptable’ risk is 50%, or lower, then the diode laser and IPL devices can be safely used for all skin colours up to about 4 – that is up to 33% melanin concentration. However, the graphs appear to indicate that these devices should be used on darker skin colours with great care – i.e. proper skin cooling.
The Alexandrite laser fares the worst – due to its wavelength being so strongly absorbed by melanin. The 50% safety criteria suggests that these lasers should be used only on paler skin colours (up to a maximum of ‘3’), unless plenty of cooling is also used.
Conclusions
The risk graphs only serve to indicate where the risk of epidermal damage is greater. Like all risks, these can be mitigated - with proper skin surface cooling. If sufficient cooling is applied BEFORE the light energy is fired, then the risk of epidermal damage can be significantly reduced. Skin cooling AFTER the application is also necessary since our calculations reveal that more than 90% of the applied energy is not used to cook the hairs!
In summary, when trying to remove hair or blood vessels with light energy, we run the very real risk of damaging the epidermis. However, this can be properly managed if good skin cooling is also applied.
________________________________________________________________________ 181 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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