Page 67 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Selective Photothermolysis
Chemical denaturation
laser wavelength
tissue absorption coefficients tissue thermal properties
absorber and target size geometry
activation energy (temperature) denaturation time
tissue’s intrinsic Arrhenius parameters
Table 10 - The parameters required for stage 1 (SP) and stage 2 (chemical denaturation).
Hair thickness is not particularly important. Thin hair loses heat more rapidly compared with
Permanent hair removal by laser or IPL is not easy. But it is achievable, if the processes are fully understood and the correct parameters are chosen. Unfortunately, our 35+ years’ experience as laser researchers/trainers have revealed that many laser/IPL users do not really know how to achieve the best from their equipment. This is a serious issue, and not just for laser hair removal.
Depths of the bulge and bulb in hair follicles
The depths of the bulge and the bulb are important in determining the required threshold (minimum) fluences needed to destroy follicles irreversibly. Computer model calculations have shown that these threshold fluences are, in many cases, sufficient to induce cell death in those
________________________________________________________________________ 67 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2025
thicker hair. But, due to their lower mass, thin hairs will achieve higher temperatures than thicker hairs, for the same incident fluence. But, our computer models have shown that a sufficient fluence will easily denature both thick and thin hairs, if suitably high.
But if those parameters are chosen properly, then all hair can be safely and effectively removed permanently, by completely destroying the stem cells.
Figure 29 - The amount of cell damage, represented by Omega, determines whether a tissue can regenerate. If more than 63.2% of the cells are irreversible denatured,
then that tissue has very little chance of recovering