Page 35 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Wavelength (nm)
SC1
SC6
600
19
2.3
755
19
2.2
810
18
2.2
1064
17
2.1
Table 7 - Ratio of hair melanin concentration to skin melanin concentration
Interestingly, the wavelength doesn’t appear to matter too much, across the skin colours. For a very pale skin colour (SC1) the ratio of melanin concentration between dark hair and the skin colour is around 18 to 19, whereas it is only around 2.2 for very dark skins (SC6). Essentially, this means that the hair on a pale skinned person is about 18 times ‘darker’ than their skin colour – for ‘black’ hair – obviously this is lower for lighter coloured hair. But for a very dark-skinned person, the hair is only about twice as dark as their skin!
Darkly pigmented skin contains more melanosomes (pigment granules) than lighter skin tones. These can be distributed throughout the full thickness of the epidermis (Figure 4).
Consequently, more light energy will be absorbed in the epidermis of a dark-skinned individual compared to a lighter-skinned person.
This tells us that the darker skins will absorb more of the energy from these wavelengths by a factor of around 8 meaning that very dark skin is 8 times more likely to ‘burn’ than very pale skin, for the same applied fluence. It also suggests that skin cooling is much more critical for darker skins...
Measurement of epidermal melanin content
The crucial challenge in light-based skin treatment is to understand and handle the light absorption in the epidermal melanin. The majority of side effects is caused by a mismatch between used light exposure settings and the actual light absorption in the epidermal melanin. It is not possible to make an accurate estimate of the percentage light that is absorbed in epidermal melanin by visual inspection. The main reason for this inability is due to the fact that our eyes’ sensitivity is non-linear. It even is difficult for the eye to make accurate quantitative 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 these treatments is to estimate the "skin colour type" according to the Fitzpatrick skin typing scale I-VI (pale to dark) which is a disaster.
________________________________________________________________________ 35 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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