Page 189 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
And this is very interesting...
There is clearly a significant difference between these two techniques. The SHR technique builds up a substantial amount of heat energy in the full treatment area, while the stamping technique delivers just one, large pulse of energy – sufficient to generate enough heat to cook the stem cells in the follicles.
The SHR technique cannot do that – the fluence is too low. So, how does it work? Well, the researchers suggest that the surrounding dermis is slowly heating up due to the high number of passes. As a result, the follicles, which do get much hotter than the dermis, cannot cool so quickly. They postulate that this means that the follicles stay hotter for longer, resulting in cooking of the stem cells.
We thought we’d test this idea in our computer model – which Mike had created to study the effects of heat generation in the skin and hair follicles.
To our surprise, they were correct!!! Even raising the background dermal temperature by a couple of degrees can make a significant difference to the outcome.
Figure 105 - SHR – if the repetition rate does not match the scanning speed, the shots will be very inconsistent leading to patchy results.
The cooking (denaturation) process is exponentially dependent on the local temperature. This means that even a small increase in temperature will induce much more denaturation.
So, if the surrounding dermis is just a few degrees warmer than normal (37C) then the follicles will cook much more easily. However, the thermal pain nerves kick in at 45C – meaning that the dermis should be kept below that temperature. This leaves only a small 8C ‘window’ to work in, to prevent great pain.
This is why the cooling is so important – without proper cooling, the skin will become too hot and the treatment very uncomfortable. So, it appears that SHR can be used successfully to remove hair, but it must be applied correctly, with sufficient cooling.
By ‘correctly’ we mean that the ‘in motion’ (or sliding/sweeping) technique must be tied to the repetition rate (Hz). This will minimise overlapping or “under-lapping”, where areas are missed, or not sufficiently heated.
________________________________________________________________________ 189 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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