Yale researchers have developed a sunscreen, made with bioadhesive nanoparticles, that doesn’t penetrate skin. They report in a new study that by encapsulating padimate O, the sunscreen enhances UV protection, while preventing epidermal cellular exposure to chemical UV filters and the health concerns associated with their direct cellular exposure.

The bioadhesive nanoparticles, according to the study’s abstract, are “readily suspended in water, facilitate adherence to the stratum corneum without subsequent intra-epidermal or follicular penetration, and their interaction with skin is water resistant, yet the particles can be removed via active towel drying.”

Most commercial chemical sunblocks, according to a Yale press release on the study, can penetrate the skin and go into the bloodstream, possibly causing hormonal side effects and promoting skin cancer.

"Almost all of the organic sunblock molecules are not chemicals we want penetrating into the skin, or into the bloodstream. Many of these are aromatic compounds that can very effectively absorb UV energy, but concerns have been raised regarding their potential to act as allergens, to release oxidative species after UV exposure and to partially bind to hormone receptors,” study coauthor Michael Girardi, M.D., professor of dermatology at Yale Medical School told Dermatology Times. “The advantages of using chemical sunblock to protect against UV damage nonetheless outweigh the risks. Our goal with the nanoparticle formulation strategy is simply to further increase the benefit-to-risk ratio."

“Nanoparticles are large enough to keep from going through the skin’s surface, and our nanoparticles are so adhesive that they don’t even go into hair follicles, which are relatively open,” Dr. Saltzman said.

The researchers used mouse models to show their sunblock protects the skin as well as commercial sunscreens, despite using significantly less active ingredient. They also studied the chemical change that occurs when sunscreens’ active ingredients absorb
UV light, called reactive oxygen species, suggesting that if these agents penetrate the skin, the resulting chemical change could cause cellular damage and potentially facilitate skin cancer, according to the release.

“Commercial chemical sunblock is protective against the direct hazards of ultraviolet damage of DNA, but might not be against the indirect ones,” said Dr. Girardi. “In fact, the indirect damage was worse when we used the commercial sunblock.”

They tested penetration levels of the Yale-developed sunscreen by applying adhesive tape strips to skin previously treated with either commercial sunscreens or the study sunscreen and removed the tape rapidly. They found traces of commercial sunscreen deep within the skin, but the study sunscreen came off entirely on the strips.


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