Page 34 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
It’s because the manufacturers want to reduce the risk of you damaging your patient’s/client’s skin – which is fair enough. But, by reducing the fluence, they are also reducing the chances of success!
What they should be telling you is that darker skins require much more cooling than lighter skins – before, during and after the treatment.
We calculated the instantaneous basal layer temperature rises in light (SC1) and very dark (SC6) skins when hit with a 20 J/cm2 fluence at the surface. We looked the difference between the alexandrite, diode and Nd:YAG lasers. Notably, maximum temperature achieved for the palest skin colour (SC1 with a melanin concentration of less than 10%) is marginally above the background dermal temperature of 37oC.
However, in very dark skin (SC6 with a concentration of >43%) the temperatures range from 54.4oC for the Nd:YAG laser to 184oC for the alexandrite laser! It was 133oC for diode lasers (see Figure 6). [Note that these are the ‘instantaneous’ rises in temperature which assumes no conduction during the pulses. In reality, longer pulses will allow for some of this heat energy to diffuse away from the epidermal melanin while the light energy is being delivered, reducing the peak temperature – so these figures represent a ‘worst case’ scenario.]
Obviously, all the other skin colours are between these two extremes. So it is very clear that while all the current hair removal lasers are perfectly fine when treating very pale skins, only the long-pulsed Nd:YAG should really be considered safe when treating black skin. We should point out that the Nd:YAG laser can be used on all skin colours!
Figure 6 - Temperature rise in the basal layers when treated by 20J/cm2 from three lasers.
The main problem appears to be that sufficient cooling to very dark skins, where the most appropriate fluence is applied, may not protect it well! This is simply because those darker skin
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