Page 114 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
after the initial consultation – it is imperative that you continually check with your clients/patients for any new relevant information!
A good report on this topic is ‘Immediate skin responses to laser and light treatments: Therapeutic endpoints – How to obtain efficacy’ by Molly Wanner et.al.
In some cases the surface hairs can be seen to vapourise – small puffs of smoke are visible. This is fine! It merely shows that the melanin in those hairs have absorbed sufficient energy to destroy them completely, However, this does not necessarily mean that the final result – destruction of the follicles – is guaranteed. It does generate a ‘burned hair’ smell in the treatment room, which has been found to be potentially hazardous! (See Section ‘Plume in the Air’.)
In summary, for most situations with laser/IPL hair removal, we are looking for some erythema and a little oedema within a few minutes of the treatment exposure. Cooling should always be applied soon after the treatment to help reduce these effects and any pain.
Threshold Denaturation Fluences – Four Devices
What are the threshold (minimum) fluences required to destroy hair follicles?
This is not easy to determine! It depends on the type of device you are using – IPL, diode, alexandrite, Nd:YAG laser. It also depends on the depth of the follicles and on the hair colour. We built a computer model to try to calculate these fluences. It considers all of the above for each device. First, we should consider what we are actually trying to do...
To effectively kill hair follicles, we need to essentially ‘cook’ the germ/stem cells, irreversibly, so that they cannot regrow. To achieve that, we must apply a certain amount of energy over a certain time – just like any cooking process!
So, we need to find the minimum amount of heat (light) needed to cook these cells properly.
IPLs – Threshold fluences
Our model allows us to apply different fluences over different pulsewidths to hair follicles at various depths. Here is what we found (for IPLs for an averaged wavelength, equivalent to 818nm) - Figure 55.
The depths used here are for the bulge, where the stem/germ cells reside on the follicle wall surfaces.
These fluences assume a pulsewidth between 2 and 50 ms. Shorter, and longer, pulsewidths will not work so well – the cooking is less efficient – but this is only for fluences up to the threshold
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