Page 59 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Hair Colour vs Skin Colour – How are they related?
Hair colour comes from melanocytes in the follicle and is generated during the anagen phase of growth. Many factors have an effect on the amount and concentration of melanin produces including age, state of health, body site, hormonal issues etc. But, in general, the melanin concentration in the hair is typically greater than found in the basal layer of the skin (except when considering grey and white hairs!)
The difference in concentration between hair and the skin depends on both the hair colour and the skin’s natural colour. The ratio between these can be seen in Table 7:
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!
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
________________________________________________________________________ 59 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022