Page 124 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
stem cells in the bulge (see section ‘Heat Transfer in the Hair follicles’ later) reveal that the pulse duration makes little difference in the final temperature-time history of the stem cells! This is because the heat energy essentially ‘homogenises’ as it diffuses out to the bulge, regardless of the peak temperatures in the hair.
But, if we were to use a longer pulse, with the same energy (fluence) will it be less painful since the peak temp, and rate of increase is lower? In addition, will the skin tone (melanin concentration) have some influence on the pain sensation?
Figure 73 – The same applied total energy can induce either high or low peak temperatures, depending on the time taken to apply it –
note all the blue shapes represent the same total energy
We are trying to ensure that the epidermal cooling rate is faster than the epidermal heating rate. If this succeeds, then the peak temperature in the basal layer and the pain will be reduced.
The cooling rate depends on the cooling efficiency - ice packs are best, with gel on the skin!
The heating rate depends on the fluence and pulsewidth (power density).
________________________________________________________________________ 124 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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