Page 158 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Anagen – catagen – telogen timings
The timings of each phase of the growth cycle are important when considering photothermal treatments. Given that such treatments appear to be successful during the anagen phase, we need to understand the growth cycles and how to ensure the correct intervals between repeat sessions.
30 70 10 52 500 2-4 70 30 12 16 65 3.5-4.5
80 20 16 12 80 2-4
Table 28 - Data from Richards-Merhag & Lynton Lasers
We can see from the above table (Table 28) that the follicle depths vary between 1 and 7 mm, depending on body area. We also know, from Section 3.1, that the fluence applied at the skin surface drops exponentially as it propagates into the skin.
Consequently, the fluence required at the skin surface must be determined by the follicle depth – or, more accurately, the depth of the stem cell bulb, which varies according to which part of the anagen phase it is in.
Clearly, as the bulb depth increases, so the applied surface fluence must also increase, to ensure sufficient energy reaches the stem cell depth. To protect the upper layers properly, we must also increase the amount of surface cooling, commensurately.
It is a ‘balancing act’ – the more fluence applied at the skin surface, the more cooling must also be applied – before, during and after the treatment. See the sections on ‘Skin Cooling’ for a more detailed discussion on this very important topic.
________________________________________________________________________ 158 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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Body Area
% Resting Hairs Telogen
% Growing Hair Anagen
Duration of Telogen (weeks)
Duration of Anagen (weeks)
Follicle Density (per cm2)
Follicle Depth (mm)
Chin
35
65
6
8-20
500
1-2.5
Upper Lip
Arm Pits
70
30
12
16
70
3.5-5
Bikini
Arms
Legs & Thighs
80
20
20
16
60
2-4.5
Breast
70
30
12
8-12
65
2-4
Scalp
10-15
85-90
12-16
2-6 years
125-200
5-7