Page 18 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
8. Many people complain about the pain during hair removal. This is caused by the thermal pain receptors (nerve endings) being triggered by the high temperatures. Those receptors are triggered at 45oC (as found by NASA). This is the same for virtually everyone.
9. The normal dermal temperature is usually around 37oC. So, it only takes an 8oC increase in temperature to induce pain! These pain receptors are located at the top of the dermis, just below the basal layer of the epidermis. This means that if the basal layer (where most of the melanin is found) becomes hot, then the pain receptors will trigger.
10. As a direct consequence of this biology, we need to cool the skin surface to minimise the pain sensations. If sufficient cooling is applied before, during and after the treatment, then the pain felt by the recipient will be much less (than if no cooling is applied).
11. Another interesting fact about light-based hair removal is that the vast majority of the light energy does NOT do the job we are attempting. Calculations shows that more than 90% of the light energy is essentially wasted! This energy will be absorbed by other constituents of the skin and cause their temperatures to rise. Surface skin cooling is critical in removing as much of this wasted energy as possible!
Figure 1 - Hair removal systems and their place in the spectrum
12. So, now we have hot hairs. What happens next? Well, heating the hairs themselves will not kill the follicle. To do that we need to kill the germ (stem) cells which cause the follicle to grow. These cells are found in the ‘bulge’ of follicles.
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