Page 41 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Light Absorption in Epidermal Melanin
All skin types (besides albinos) have some melanin in the epidermis. The amount of epidermal melanin can range from about 2% (by volume) in very pale skin, and up to more than 43 % in dark skin. The melanin is produced in cells called melanocytes present in are the basal cell layer (the bottom layer of epidermis. Note that the thickness of epidermis typically is less than 0.1 mm which is about the thickness of ordinary copy paper. There is no blood present in the epidermis as there are no blood vessels there.
When skin is exposed to light a portion of the light will be absorbed in the epidermal melanin and heat it up. The more melanin, the shorter wavelength, the more heat. The absorption of melanin is very wavelength dependent. The shorter wavelength the higher absorption i.e. blue light creates much more heat in the melanin compared with red light at equal fluence and pulse duration settings, see graph below.
Figure 11 – The fraction of light absorbed by melanin depending on wavelength
The majority of side effects in light-based skin treatments are caused by skin burns due to overheating of the epidermis. Avoiding overheating of epidermal melanin is actually your biggest challenge in light-based treatments. The only way to control and avoid overheating of epidermal melanin is to:
A: Accurately measure the amount the epidermal melanin at the actual treatment site.
B: Provide consistent and depth selective cooling of the epidermis.
C: Understand the parameter settings of the specific light source used.
We will later cover these three extremely important topics in detail later but first we will continue explaining the fundamental optical properties of the skin.
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