Page 58 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
How the anatomy of target and absorbing tissue determines the pulse duration
For every specific treatment there exists an optimal combination of treatment settings i.e. fluence level, wavelength and pulse duration as well as skin pre-cooling conditions. The optimal pulse duration is fundamentally governed by the size and anatomy of the target tissue and the adjacent chromophore-rich light absorbing tissue.
If we take a closer look at hair reduction we can distinguish the both size and anatomical configuration in follicles, see Figure 21 – The real target in the hair follicles are the germ/stem cells found in bulges on the follicle walls. Both the diameter of the hair shaft and the follicle are important, in these considerations.
The optimal pulse duration can be estimated from the maximum distance between the absorbing tissue (melanin in the hair shaft) which contains the chromophores and the tissue targets (the germ cells). This implies that there is need to destroy the absorber tissues – the hairs. In fact, the absorber tissue should be kept more or less intact during the heating cycle /pulse duration in order to preserve the light absorption properties in order to convert light energy into heat.
We don’t really want to destroy the hair shaft itself – just the germ cells!
In treatment of hair the real target tissues are the stem/germ cells located outside of the follicles outer root sheet in the bulge region.
Clinical studies show that a normal sized follicle with well-pigmented hair requires a fluence of 20 J/cm2 in order to cook/coagulate the stem cell target tissue. Hair shafts with less pigment, such as light brown or blonde, require substantially higher fluences as the concentration of melanin is significantly lower, leading to less heating in the hair.
________________________________________________________________________ 58 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022