Page 114 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
temperatures of the hairs, but don’t really have much influence over the timings in the stem cells.
Our research shows that the fluence has a more significant influence on the outcome than the pulsewidth. Once that threshold fluence has been exceeded, the pulsewidth becomes less important. As the fluence increases above the threshold, the influence of the pulsewidth becomes less relevant.
This indicates that we should probably focus more on the applied fluence rather than the pulsewidth when treating hair – whilst keeping the pulsewidth within ‘safe’ limits. Too long a pulse will inevitably cause unwanted damage to the adjacent tissues.
Figure 64 - The target melanin is located in the hair shaft and in the bulb
At present, our results show that keeping the pulsewidth in the range from around 5 to 50 ms is a ‘safe zone’ – a supra-threshold fluence will always successfully denature the stem cells. Again, we should remember that the fluence has an upper limit too – otherwise damage is likely.
As fluence is increased, the importance of pulsewidth diminishes, significantly!
This is due to the fact that the target cells will denature exponentially faster at higher temperatures, thereby requiring much less time in which to do so! (See the section on the ‘Arrhenius Equation’.) This is a very recent discovery and, as such, is not well known yet.
________________________________________________________________________ 114 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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