Page 78 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Anagen - active growing phase – weeks to years Catagen - transitional phase – up to 2 weeks Telogen - resting phase – 10 to 20 weeks
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 10 - Data from Richards-Merhag & Lynton Lasers
We can see from the above table (Table 10) 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 germ cell bulge.
Clearly, as the follicle depth increases, so the applied surface fluence must also increase, to ensure sufficient energy reaches the germ cell depth. To protect the upper layers properly, we must also increase the amount of surface cooling, commensurately.
________________________________________________________________________ 78 Chapter 3 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