Page 33 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Let’s consider the skin colour. There are two important issues we should think about:
1. The melanin in the basal layer will absorb light energy, inducing a temperature rise in that layer. This heat will diffuse towards the thermal pain receptors (just below the basal layer) and trigger them. If the temperature is high (above 45oC), then pain will be felt.
2. Any fluence absorbed in the basal layer will not be available to the deeper melanin in the hair shaft. So, darker skins will result in lower fluences reaching the hair melanin.
So we have a conundrum...
To successfully kill the hair follicles we must apply a certain minimum fluence at the skin surface. But the skin’s natural colour will absorb some of this fluence, leading to higher temperatures at that depth. This suggests that darker skins will require more surface cooling to minimise potential damage in the epidermis.
Most laser/IPL devices have a “Skin Type” selection option - usually when a higher skin type is chosen, the fluence automatically decreases. This is entirely WRONG!!!! For two reasons:
Firstly, the darker skin will ‘lose’ more fluence because of the higher absorption in the basal melanin;
and secondly, applying a lower fluence at the surface will reduce the likelihood of a successful treatment!
In reality, we should consider the following:
The fluence MUST be chosen to match the colour and depth of the hair;
The skin colour MUST dictate the amount of surface cooling!
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?
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