Page 69 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 31 – The real target in the hair follicles are the germ/stem cells found in bulges on the follicle walls
The minimum fluence that would provide permanent hair reduction (i.e. complete destruction of the total stem cell volume) is in the range of 9-11 J/cm2 for very dark hair on pale skin (for diode and Alex lasers and IPLs) – but this is only for shallow follicles (this is closer to 25 J/cm2 for Nd:YAG lasers). As the follicle grows, and descends to the fatty layer, the stem cells in the bulb become more difficult to kill. Consequently, higher fluences are required to successfully destroy those deeper follicles, when they are anchored in the sub-cutis. (We discuss this in more detail in the Section ‘Our Computer Models – What are the ‘optimum’ fluences?’ and list these fluences in Table 22).
Hair depth and fluence
It has been found that the depth of hair follicles range across the body quite significantly. In the upper lip they are typically between 1.5 and 2.5 mm deep, whereas in the axillae (arm pits) and bikini regions they may be down to 4 mm deep (Richard and Merhag).
This means that we must consider using different fluences when tackling different regions of the body. If a fluence has been chosen for the upper lip, to reach follicles at a depth of 2.5 mm, then this fluence will not be sufficient for a bikini or axillae region – the fluence will simply not be enough to heat up the melanin in the bulb in those deeper follicles properly!
________________________________________________________________________ 69 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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