How does UV radiation create a sun tan?
(Excerpted from US Patent 4967090) Skin pigmentation and thickening of the upper layer of the skin called the corneum are the body’s natural protective reactions to exposure to .ultraviolet energy produced by the sun; these reactions are the skin’s defense against further assault. Skin pigmentation, or tanning, is the result of a complex biological process, and to understand it, one most understand the skin’s response to different wavelengths of ultraviolet radiation. Deep down in the skin are special cells called melanocytes. Once these are stimulated with ultraviolet light, they will utilize substances which they have stored up to produce the pigment melanin. Because these substances only absorb .(UV B) ultraviolet light, these UV B rays must be present in order to achieve melanin production. Longer wavelength ultraviolet (UV A) can also formulate melanin but only when there exists enough sensitizing material in the skin to bring about a UV B-type reaction. However, this requires a v
