Page 23 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
However, when trying to kill hair follicles, it’s a little bit more complicated...
The real targets are the germ cells. But they don’t have any target in them that we can directly heat with a careful choice of wavelength and fluence. So, we must use a ‘surrogate’ – the melanin in the hair shaft. We heat up the melanin and allow diffusion of heat to the germ cells to do the rest.
But, we don’t want to destroy the melanin - i.e. we don’t want to over-cook the melanin by applying too much energy, otherwise we will destroy our friendly little surrogates.
So, we must choose a pulsewidth which will not cause the melanin to overheat, whilst also allowing sufficient heating to cook the germ cells.
This is not an easy calculation!!
We designed a computer model to study this exact scenario. In the model, we raise the temperature of the melanin in a hair shaft, over the pulsewidth, and watch as the heat energy spreads out to the germ cells, on the walls of the follicle (these can be quite far from the melanin in the hair shaft).
By changing the fluence and/or the pulsewidth we can calculate which set will result in the desired outcome – the total ‘cooking’ of those germ cells.
It turns out that we should always apply a pulsewidth between 5 and around 40ms to achieve the best results. The fluence depends on how deep those follicles are. Deeper follicles require higher fluences (which, in turn, requires more skin surface cooling to mitigate).
This is quite a tricky topic. We will discuss it further later in the book.
The above are the three most important parameters (settings) which must be carefully selected to ensure good results. If any one of them is not correctly chosen, then the chances of success are greatly reduced.
Table 2 – Basic laser/IPL parameters
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