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In the last 2 years I have heard at least 3 presentations given by "experts" on various topics of photoprotection and sunscreens. The speakers were faithful to the traditional classification of sunscreens as "chemical" and "physical," referring to the solubility or insolubility of the particles. Yet these labels seem to promote a misperception regarding how and why sunscreen agents protect the skin. The effectiveness of a sunscreen agent is based on its ability to absorb the selected wavelengths of light, whether in the visible (400- to 700-nm), UV-A (320- to 400-nm), or UV-B (280- to 320-nm) range.

The labels physical and chemical as applied to sunscreens are inappropriate. Materials such as titanium dioxide (TiO₂), zinc oxide (ZnO), iron oxides, barium sulfate (BaSO₄), magnesium oxide (MgO), and talcum powder remain as particles when introduced into a vehicle because their solubility is very low in acceptable dermatologic preparations. These substances . . . [Full Text of this Article]