Page 160 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Hair colour vs absorption
The amount of light which will be absorbed by hairs of different colours will depend very strongly on that colour. The table below shows this variation:
Hair colour
Black Brown Blonde Grey/White
Melanin concentration
Very high High Low Very low
Absorption
Vert strong Strong Poor Very poor
The above absorption assumes a typical ‘red’ wavelength.
Visible Hairs – which phase are they in?
This is an interesting question which most people don’t really consider. Most people probably assume that all visible hairs are in the anagen phase – actively growing. But that’s not true. A percentage of them must be in the catagen phase and another percentage in the telogen phase. But, to the human eye, there is no difference between them!
Then there is an added complication following laser/IPL treatments. Some of the follicles will not have been destroyed – they will have merely been ‘stunned’. Research has shown that these follicles are usually forced into an early ‘catagen-like’ phase, followed by a ‘telogen-like’ phase. If the hair shafts have survived the treatment, then, again, they are difficult to determine.
Anagen
Catagen Telogen Catagen-like
Telogen-like
These hairs must be in either A5 or A6 stage of growth, to be visible above the skin surface. The hair shaft is fully formed and melanised. The bulb is located in the subcutis and is also melanised. (Chase, Uno, Bouabbache)
The bulb begins to lose it melanin as the follicle regresses. (Chase, Roosen)
The bulb is lacking melanin completely, while the hair forms a club hair. (Chase, Alonso and Fuchs)
Induced by thermal damage, the anagen hair is ‘forced’ into an early catagen-like stage, with evidence of trauma in the DP and matrix cells. (Town, Roosen, van Vlimmeren)
Induced by thermal damage, the follicle becomes quiescent, with no melanin in the bulb (Gan and Graber).
________________________________________________________________________ 160 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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