Page 41 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
The fluence applied to the skin surface should NEVER be set according to the skin colour – that defeats the whole purpose of the treatment. And yet, many of today’s devices are programmed to do precisely this.
Why?
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 YOUR 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 11). [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!
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 types contain so much melanin that the temperatures generated are too high for surface cooling to have the desired effect. In such cases, we recommend using the long-pulsed Nd:YAG laser as it will generate the lowest peak temperatures in the basal layer (see Figure 11).
Using an IPL with the wrong filters will also induce very high temperature in darker skins (see the section ‘Choosing the Correct IPL Filter’).
What these calculations show is that surface skin cooling is critical as the skin colours darkens – whether it’s a ‘natural’ skin colour or a tan. It is an unfortunate fact of physics that a small
________________________________________________________________________ 41 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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