Laser Hair Removal: Comparative Study of Light Wavelength and its Effect on Laser Hair Removal
Cheung, Ling; Mitrea, Diana; Suhrland, Cassandra; Zeng, Henry
For some people, hirsuteness (having excess body hair) can be an embarrassing problem. Many attempts have been made to find a solution to these problems, including electrolysis, tweezing, shaving, and waxing. However, most of these solutions are painful, are not useful in treating large areas of skin, or are not permanent. Laser hair removal stands out amongst these other methods as a permanent method of reducing hirsuteness that can cover large areas of the body, such as the chest or the legs. While laser hair removal is a widely used technology, few studies have explored the physical aspects of why it works so well. More specifically, there is a significant lack of computer models that show how temperature profiles look inside the hair and surrounding skin. Using the physical properties and dimensions of hair, we constructed a model of the hair that approximates how actual hair resides in the skin. Using COMSOL Multiphysics, we tested this model with five different lasers of varying wavelengths in order to determine the relationship between laser wavelength and temperature in the hair. Using a laser pulse duration of 0.01 seconds (10 milliseconds), we found a positive correlation between wavelength and temperature, with all wavelengths except the lowest (595 nm) achieving a temperature above the threshold temperature required for hair destruction. In addition, while all lasers caused a temperature rise in the surrounding skin, the extent of thermal damage was minimal. However, since we could not find physical properties of the hair follicle itself, we were forced to approximate those properties using the hair shaft properties, ultimately leading us to treat the follicle and shaft as one entity. This is a slight limitation with our design. Regardless, we have provided a greater understanding of the physiological temperatures involved in hair removal, and have reinforced the fact that laser hair removal can be a safe method and effective method for treating hirsuteness by showing that hair follicles can be heated to a temperature that kill them by using lasers, and that this heating does not severely or irreparably damage surrounding skin.
Laser; Hair removal; Wavelength
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