Page 35 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
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 6).
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 increase in fluence results in a large (exponential) increase in tissue damage – which is great when trying to destroy germ cells in follicles, but not so good when we consider the epidermis.
Conclusion
The bottom line is that we are trying to remove hair permanently from people’s skin – across a wide range of skin colours. The science shows that to do this we MUST apply the correct fluence, which depends on the hair colour and depth. It does NOT depend on the skin colour - that is completely unrelated to the actual treatment.
But the skin colour is directly related to epidermal damage and pain. To alleviate the pain sensations we must apply plenty of cooling – before, during and after the treatment. This will suck much of the excess heat energy located in the basal layer (which is not that far from the surface!), resulting in much lower temperatures there (see Figure 7).
Figure 7 – When treating three skin colours (SC1,3 and 6) the amount and concentration of melanin in the epidermal basal layer determines the maximum temperatures that may be achieved there. In the above case a fluence of only 20J/cm2 from a diode laser may generate temperatures from 38.6 to 133oC (instantaneously).
We know this will go ‘against the grain’ of current thinking, but the physics is very simple. Reducing the fluence to ‘compensate’ for skin colour is quite wrong!!
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