Page 60 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
estimates of the darkness/light absorption on a grey scale and it is even more difficult for objects with different colours.
As mentioned before the dominating procedure in SPT treatments is to estimate the "skin colour type" according to the Fitzpatrick skin typing scale I-VI (pale to dark) which is a disaster.
The vast majority of people treated with SPT belongs to skin type range I-IV. Skin type VI can only be treated in safe and effective manner using an Nd:YAG laser. Skin type V can sometimes be treated by a very skilled therapist for hair removal but not for any other types of skin indications.
In the skin type range I-IV only Fitzpatrick skin type I safely can be judged visually. The melanin content/absorption of skin type II-V must be measured with an appropriate optical skin reflectometer device, to be certain.
Note that it is not the colour of the skin that is of interest, it the amount of light absorption that has to be measured. Two quite different skin colours can in fact be equal in terms of epidermal light absorption.
Absorption %
Light absorption % in Epidermal Melanin vs Fitzpatrick skin type
45
40
35
30
25
20
15
10
5
0
123456
Fitzpatrick Type
Low abs
High abs
Average
Figure 22 – How much light energy does the epidermis absorb?
From the diagram above you can see why the Fitzpatrick skin typing system is so inaccurate. The actual light absorption in epidermal melanin for each specific skin type typically diverge a factor of 2. For example, in skin type III the melanin light absorption range is between 4-8 % i.e. a factor of two between low and high. The implication of this variation is that you cannot use standard device settings in terms of fluence / pulse duration, light colour, for each specific Fitzpatrick skin type.
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