Page 124 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The graphs (Figure 60) show that the long-pulsed Nd:YAG is, by far, the safest option when considering epidermal damage, for all skin colours. The maximum risk, with this wavelength (1064nm) is only 30% (compared with 100% for the alex/black skin combo), meaning that the alexandrite laser is more than three times more likely to induce unwanted damage than the Nd:YAG laser.
If we assume that an ‘acceptable’ risk is 50%, or lower, then the diode laser and IPL devices can be safely used for all skin colours up to about 4 – that is up to 33% melanin concentration. However, the graphs appear to indicate that these devices should be used on darker skin colours with great care – i.e. proper skin cooling.
The alexandrite laser fares the worst – due to its wavelength being so strongly absorbed by melanin. The 50% safety criteria suggests that these lasers should be used only on paler skin colours (up to a maximum of ‘3’), unless plenty of cooling is also used.
Conclusions
The risk graphs only serve to indicate where the risk of epidermal damage is greater. Like all risks, these can be mitigated - with proper skin surface cooling. If sufficient cooling is applied BEFORE the light energy is fired, then the risk of epidermal damage can be significantly reduced. Skin cooling AFTER the application is also necessary since our calculations reveal that more than 90% of the applied energy is not used to cook the hairs!
In summary, when trying to remove hair or blood vessels with light energy, we run the very real risk of damaging the epidermis. However, this can be properly managed if good skin cooling is also applied.
What are the settings we must choose and why?
There are five parameters (settings) we must consider when treating hair with a laser or an IPL (see Figure 61). These are wavelength, pulsewidth, fluence, skin cooling and skin pressure – this last ‘setting’ only applies to those systems which are in physical contact with the skin surface such as diodes and IPLs.
Wavelengths
This is easy – virtually all modern photothermal systems used for hair removal use red and infrared light energy. The main reason is that these wavelengths are reasonably well absorbed by melanin, but can penetrate deep into the dermis without damaging blood vessels.
________________________________________________________________________ 124 Chapter 3 Laser/IPL Hair Removal
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