Page 123 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 72 - Here we see how the temperatures of the hair shaft wall (orange) and the follicle wall (blue) vary as we increase the pulsewidth from 10 to 300ms for a 10 J/cm2 fluence on a 180 μm diameter hair. The grey curve shows the corresponding change in the amount of denatured stem cells (Omega). (Note – the x-axis is not linear.)
Further research has shown that this effect is even more pronounced with higher fluences. As the fluence increases, the importance of the pulsewidth becomes less and less relevant.
Mike presented this information at the BMLA conference in Liverpool, 2024. You can see his presentation here:
The important point to take away from this section is that the pulsewidth is really not so important in these treatments. The fluence is much more critical.
Should we use longer pulses to reduce the pain in LHR?
We need to apply a certain amount of energy to achieve the desired result. The pulsewidth determines the power of this energy.
A short pulse will induce a higher peak temp in the hair shaft and epidermis – more pain sensation may be felt, as a result. But, calculations of the heat flow from the hair shaft to the
________________________________________________________________________ 123 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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