9.6.3　Sunscreen products

UV absorbents are active ingredients in sunscreen products that prevent harmful UVB（290-320 nm）and UVA（320-400 nm）from reaching the active layer beneath the skin's surface.To enhance efficiency，UV absorbents must be retained on the uppermost surface of the skin as a protective film and should also remain photostable throughout the entire UV exposure period.Skin penetration and photolysis of UV absorbents are undesirable since skin penetration decreases expected UV protection while photolysis leads to changes in color and appearance，and increases phototoxicity of the sunblock.And decomposed products of UV absorbents may leads to allergies.

The most popular UV absorbents are lipophilic molecules with relatively low molecular weight.Although measures are taken to promote photostability，such as addition of photostabilizers and use of high molecular weight UV absorbents to minimize skin absorption，they still are capable of penetrating skin and being systemically absorbed.Thus，developing innovative formulations of non-penetrating UV absorbents is still necessary.(https://www.daowen.com)

Under the circumstances，encapsulating UV absorbents in different structured materials is a useful strategy to prevent skin penetration and enhance the photoprotective potential of sunscreen actives.Encapsulation encompasses many supramolecular systems，such as solid lipid NPs，nanostructured lipid carriers，nanoemulsions，polymer NPs，silica NPs，and dendrimers.This section provides a brief description of the novel nanocarriers which are being used for sunscreen products.