Page 108 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
depths are typically halfway down the follicle below). Deeper bulges require more fluence to ensure success.
Area
Max follicle depths (mm)
Max bulge depth (mm)
Upper lip
2.5
1.25
Chin
4
2
Arm pits
4.5
2.25
Pubic
5
2.5
Arms
4
2
Legs
4.5
2.25
Scalp
7
3.5
Table 14 – The maximum bulge depths are typically halfway down the follicle
Clinical studies indicate that follicular bulges are around one third to one half of the depth of the full depth of hair follicles. We calculated the threshold fluences for each body area above based on the deeper option – 50% of the depth.
It becomes obvious that using the same fluence on a patient’s upper lip will not have the same effect if used on their arms or legs, simply because those follicles are deeper!
So, what are these minimum fluences that we need to use?
We built a computer model looking at the temperatures generated by different wavelengths at different depths in the skin.
Error! Reference source not found. shows the required minimum fluences to successfully denature the germ cells in a number of body areas. These are all based on the depths of those bulges. Clearly, as the depth increases, the required fluences also increases. We can also see that the fluences increase as we go from alexandrite to diode/IPLs to Nd:YAG lasers, as a direct consequence of their absorption coefficients in melanin.
Now, we’re not saying that this model is ‘perfect’ by any means. It is only a 1-dimensional numerical analysis, but it is useful in indicating the ‘ballpark’ numbers. A more detailed model would require much more time to build – and time is precious!!
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