Page 105 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Fitzpatrick Type
Low abs %
High abs %
Average %
1
0.5
1.5
1
2
1.5
4
2.75
3
4
8
6
4
8
16
12
5
16
32
24
6
32
43
36
Table 25 – Absorption of light energy compared with skin types
Epidermal peak temperatures for three fluences
Most pain experienced in laser/IPL hair removal is directly attributed to the high temperatures attained in the epidermal basal layer where the melanin absorbs a significant proportion of the incoming light energy. This absorption depends greatly on the wavelength(s) of the light since this determines the absorption coefficients. It is easy to calculate the resultant temperature rise for each wavelength, given the fluence.
Figure 50 shows the temperatures attained for four wavelengths with an applied fluence of 10 J/cm2 at the skin surface, over six skin colours (melanin concentration ranging from 5 to 43%).
The red dotted line shows the temperature at which the thermal pain receptors in the skin activate – 45oC. It is interesting to see how the various wavelengths induce a range of temperatures in the epidermis. The alexandrite laser (755nm) induces a sub-painful temperature for skin colours 1 and 2, but then induces pain as the colour darkens. Likewise with the diode wavelength (810nm), whereas the 1064nm from the Nd:YAG laser does not begin to induce pain until skin colour 5.
Figure 50 – Epidermal peak temperatures for four wavelengths at 10 J/cm2
________________________________________________________________________ 105 Chapter 3 Laser/IPL Hair Removal
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