Page 68 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
stem cells located around the bulb region, down to a certain depth (we calculated down to a depth of 4mm, since that appears to be the deepest human hair follicles can reach).
The scientific medical literature says that the bulge is between 1/3 and 1/2 of the way down a follicle, from the surface. This is typically around 1.0 to 1.5mm from the skin surface, and does not vary much throughout the follicle’s lifetime (Ross et.al.).
Figure 30 - Depth of germ/stem cell bulge
We will later calculate the ‘threshold’ (minimum) fluences required to effectively heat the stem cells in these bulges, at the depths, to ensure that they are all irreversibly denatured.
We don’t really want to destroy the hair shaft itself – just the stem cells!
In treatment of hair the real target tissues are the germ/stem cells located on the outside of the follicles on the outer root sheet in the bulge region and in/around the bulb. The problem is that, while the bulge cells remain at a constant depth throughout the growth phase of the follicle, the bulb will descend towards the fatty, sub-cutis layer. This makes it more difficult to target effectively since, at some time, it may be too deep for the applied fluence to have the desired effect.
Clinical studies show that a normal sized follicle with well-pigmented hair requires a minimum fluence of around 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 absorption of light energy and, consequently, less heating in the hair.
________________________________________________________________________ 68 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2025