Regulatory bodies require quantifiable, photostable UVA protection for sunscreens,1,2 and zinc oxide (ZnO) provides such protection, as well as a long history of safety in sunscreens and cosmetic applications.3 Groups such as the US Food and Drug Administration (FDA) and the Therapeutic Goods Association (TGA) also have approved ZnO for use as a UV active ingredient in OTC sunscreens. Furthermore, ZnO has Generally Recognized as Safe (GRAS) status, is the only ingredient recognized by the FDA as providing both UVA and UVB protection, and is defined by the FDA as a Category I skin protectant, inferring that it can be used safely on compromised or environmentally challenged skin.
However, a drawback to formulating with ZnO is its white appearance on skin, which creates low cosmetic acceptability and marketability. This whiteness is caused by the back-scattering of light from submicron sized ZnO particles in sunscreen formulas. By reducing the ZnO particles to nanometer size (< 100 nm), product developers have successfully decreased this scattering and developed transparent formulations but such formulas are limited to approximately 5% w/w ZnO content.
