Page 145 - Chapter 3 - An Introduction to Laser/IPL Hair Removal
P. 145
Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Omega vs dermal temperature Fluence 10.7 J/cm^2, pulsewidth 10ms
Omega
80 70 60 50 40 30 20 10
0
98 96 94 92 90 88 86 84 82 80 78
Germ cell temps
37 38 39 40 41 42 43 44 45 46 47 48 49 50 Dermal temperature at start of treatment (C)
Figure 69 – 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 69 we can see that simply by raising the temperature of the dermis by a couple of degrees, the amount of germ cell denaturation increases rapidly, while maintaining the same fluence and pulsewidth.
Increased 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 37oC – the typical dermal temperature. They trigger at 45oC – meaning that it only takes an 8oC increase in temperature at that depth to make things painful! (See previous Section – ‘IPL ‘Over-heating’ – the need for proper surface cooling’).
However, if surface cooling reduces the temperatures of the nerve endings by 10oC, then you have an 18oC 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.
So, keep cooling!
________________________________________________________________________ 145 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022
