Nonionizing Radiation and the Skin
There are two important considerations regarding the optical properties of skin. First, skin optics are very complex due to the presence of a wide variety of absorbing molecules and the large number of optical surfaces available to inﬂuence the path of photons. Nucleic acids and proteins absorb the shorter wavelengths of UV radiation while melanin, a complex polymer, absorbs across the UV and visible wavebands almost like a neutral density ﬁlter. The epidermis and stratum corneum contain numerous optical surfaces. Second, the optics of skin are constantly changing as, for example, when the blood ﬂow is increased in response to a rise in temperature, or tanning occurs following exposure to UV radiation.