Page 73 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
At the base of the follicle is the dermal papilla which supplies the follicle with blood. Many believe that the target of laser hair removal is to destroy this blood supply. Clinical studies show that this is not usually the case following laser treatment. Given that most hair removal lasers use red light energy (including IPLs) the probability of heating these vessels sufficiently is very low – they simply will not absorb enough energy!
The hair colour comes from the melanin which originates in the hair matrix. Eumelanin produces black/brown hair, while pheomelanin results in red/yellow/ginger hair. Hair containing eumelanin will strongly absorb many wavelengths of light which can be exploited for laser/IPL hair removal. However, the pheomelanin absorbs red and infrared light very poorly resulting in dismal results when treated by this technology.
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 table/graph which show these results:
Figure 24 – 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....’)
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 germ cells, located on the outer follicle walls, and thermally denature them (‘cook’ them!). From Figure 24, and other data,
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