As the wavelength of laser light increases, what happens to melanin absorption in the skin?

The understanding of laser light and its interaction with melanin in the skin hinges on the principles of selective photothermolysis and how different wavelengths penetrate and are absorbed by various structures in the skin.

As the wavelength of laser light increases, the absorption of that light by melanin generally decreases. This is because melanin has a specific absorption spectrum, with its peak absorption occurring at shorter wavelengths (around 500 nm to 600 nm) where it is most effective at absorbing light. As the wavelength moves into the infrared range, which is beyond the optimal absorption range for melanin, the laser light is less effective at being absorbed.

This behavior is critical in laser treatments such as tattoo removal, hair removal, or treatment of pigmented lesions, where the goal is to target melanin without affecting surrounding tissues. Therefore, a higher wavelength results in a decrease in melanin absorption in the skin, confirming that as the wavelength increases, the loss of absorption by melanin becomes pronounced.