Page 79 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
But how much of this energy is actually absorbed by the hair? Well, going from the calculations in Table 16, it appears very little is absorbed, since the targets areas are so small!! (To be more precise, we’d have to do a volume calculation.
This would involve calculating the energy distribution in the skin, which depends on the absorption and scattering coefficients of each constituent. This approach would give a more accurate set of answers, but we suspect the actual numbers would be very similar to the above, much simpler, calculation.
So, let’s look at the maximum amount of light energy that may be absorbed in the hairs. From Table 15, it appears that the hair in the chin and upper lip will absorb around 13% of the incident light energy. But in the armpits, pubic region and legs this drops to less than 2%.
This is very surprising!!
What this tells us is that the vast majority of the light energy is not doing the job we are attempting. In fact, Monte Carlo calculations by PA, reveal that much of this light energy is either reflected or back-scattered out of the skin altogether. This can be more than 60% of the incident energy, depending on the wavelength.
Of the remaining 40%, a portion is absorbed in the hair melanin (depending on the Skin Colour). Most of the rest of it will be absorbed in the dermis where it will be converted into heat energy by other tissues. This is not good! This will cause the temperatures in the epidermis and dermis to rise, potentially damaging those tissues, and may lead to scarring.
Skin cooling before and after photothermal treatment is very important. We will discuss this in detail in Section 3.3.
Skin diseases and disorders
Many skin conditions present similar lesions. A thorough examination of the skin in good light is essential when assessing any client. Careful questioning is also essential including family background. In a number of instances accurate diagnosis is not possible without referral to the medical profession for further investigation. If you have any doubts about a client’s suitability for treatment due to the nature of their skin then you should refer the client to his/her GP/dermatologist for advice.
There are a number of skin conditions which should not be considered for treatment including (please note that the following list is not exhaustive):
________________________________________________________________________ 79 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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