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Wednesday, July 23, 2014
Skin Care and Diseases
Why does Sunscreen Tan my Skin?
I am African-American. When I use sunscreen daily, my skin becomes a deeper, darker, beautiful, dark brown. My skin does not tan as much when I am in the sun without sunscreen. Why does sunscreen affect my skin in this way?
Sunscreens are formulated to filter the ultraviolet wavelengths (290 to 400 nm) emitted by the sun. There are portions of the UV spectrum that are better filtered than others. For example, only a few sunscreen filters can absorb long wavelength UVA, and still not perfectly, as wavelengths beyond 370 nm are not completely filtered. So there could still be some UV rays that are penetrating and able to modify the character of the skin, even with sunscreen on. For example, the type of brown pigmentation you are noticing may be brought about by longer UVA wavelengths or even visible light from the sun, which also has some biologic effects. Without sunscreen, you're relying on your inherent pigmentation to filter UV, and so the natural tanning response may be different than when you have sunscreen on.
Elma D Baron, MD
Associate Professor of Dermatology
Director, Skin Study Center
School of Medicine
Case Western Reserve University