Page 191 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
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Omega vs dermal temperature Fluence 10.7 J/cm^2, pulsewidth 10ms
37 38 39 40 41 42 43 44 45 46 47 48 49 50 Dermal temperature at start of treatment (C)
Omega
Germ cell temps
Figure 106 – We ran a series of simulations in our thermal transfer model. We found that the value of Omega (which determines how denatured cells are) increased rapidly with higher background dermal temperatures.
In Figure 106 we can see that simply by raising the temperature of the dermis by a couple of degrees, the amount of stem cell denaturation increases rapidly, while maintaining the same fluence and pulsewidth.
Increasing the fluence with cooling
We have discussed skin cooling many times previously. It is critical in obtaining good results without damaging the adjacent tissues. However, another good reason why cooling is very useful is that it allows us to apply higher fluences than may be tolerated if cooling is not used.
Since the thermal pain sensors are just below the epidermis, any cooling of these nerve endings prior to application of the laser/IPL energy, will give you a larger ‘window’ of fluences to play with.
Quite simply, the normal temperature of the nerve endings will be around 37C – the typical dermal temperature. They trigger at 45C – meaning that it only takes an 8C increase in temperature at that depth to make things painful! (See Section 3.5 – ‘IPL ‘Over-heating’ – the need for proper surface cooling’).
However, if surface cooling reduces the temperatures of the nerve endings by 10C, then you have an 18C operating window. This means that you can use higher fluences before triggering the pain sensors. Higher fluences will induce higher temperatures in the follicles and, hence, generate better results overall.
________________________________________________________________________ 191 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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