Page 151 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
The deeper region of the follicle is the ‘cycling’ region – this is the part of the follicle which grows towards the sub-cutis (fatty tissue layer) and then regresses back towards the surface, after a period of time.
The duration of the anagen and telogen phases are variable across the body while the catagen phase is typically around two to three weeks in duration. The precise details of the initiation of the anagen phase are not fully understood as yet, but it is believed that external signals trigger the growth stage. Anagen 1 lasts for a relatively short time – perhaps only up to 48 hours, in most cases.
Hair Shaft and Follicle Sizes
Various studies through the years have looked at the diameters of hair shafts and follicles across the body. Below is a graph (Figure 84) which show these results.
From this data we can see that the hair shaft diameters range from as small as 8 microns (1 micron is 1/1000 of a millimetre) up to 55 microns, while the follicles diameters range from 10 to 220 microns. This wide range of sizes has a significant effect on photothermal treatments. The applied light energy must generate sufficient heat energy to reach the target stem cells, located on the outer follicle walls, and thermally denature them (‘cook’ them!). From Figure 84, and other data, it appears that the follicle diameters are typically between 3.5 and 5 times the diameters of their hairs.
Figure 84 – Hair shaft and follicle diameters across the body – the smaller bars
are hair shaft diameters, while the larger bars are the diameters of the corresponding follicles
(Data from Otberg et.al. – ‘Variations of hair follicle size and distribution in different body sites....’)
________________________________________________________________________ 151 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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