Page 92 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
This is a very recent discovery and, as such, is not well known yet.
The relation between fluence, temperature and cell damage
Human beings are quite simple creatures. Our brains are wired to think in straight or wiggly lines. But, we’re not very good at thinking about ‘exponentials’ – it’s just too weird for us! However, many things in Nature do occur exponentially – and it is better if we do understand them.
For example, laser/IPL hair removal (and other treatments) tend to work on an exponential basis. When we increase the fluence (energy density) on our devices, the amount of light energy going into the skin increases. Therefore, the amount of light absorbed by the target chromophores also increases. This light energy is converted into heat energy which raises the local temperatures.
Now, if we increase the fluences, we automatically increase the temperatures induced in the hairs. This is a simple “linear” process – the temperature increase is ‘in step’ with the increasing fluence.
Figure 44 - If we increase the fluence, the local temperatures will also increase – linearly.
But, this is where it gets a bit weird. The way cells react to increased temperatures is most definitely NOT linear – it is exponential.
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