Scientists create sunblock that doesn't go skin-deep

A sunscreen that does not penetrate the skin has been developed by a group of scientists, removing the serious health issues linked with the current type of sunblock. While most commercial sunscreens prevent sunburn effectively, they can go below the skin’s surface and enter the bloodstream, posing possible hormonal side effects and even lead to skin cancer, claim researchers at Yale.

Their findings, which appeared in the online edition of the journal Nature Materials, describe how the team created the new sunblock, which stays only on the surface of the skin. The researchers developed a nanoparticle with a surface coating rich in aldehyde groups, which sticks to the outer skin layer. The nanoparticle’s hydrophilic layer locks in the active ingredient, an organic chemical called padimate O, used in many commercial screens. By coating the padimate O with the nanoparticle, the team was able to come up with a sunblock that is both transparent and stays out of the skin cells and bloodstream.

“We found that when we apply the sunblock to the skin, it doesn’t come off, and more importantly, it doesn’t penetrate any further into the skin. 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,” explains Mark Saltzman, the study’s senior author and a professor of biomedical engineering at the Goizueta Foundation.

In a trial using mouse models, the researchers found that even though the sunscreen used a significantly smaller amount of the active ingredient than commercial variants, the team’s formulation protected equally well against direct ultraviolet, or UV rays. The researchers tested their product’s penetration levels compared with the commercial kind, by using applied strips of adhesive tape to skin previously treated with sunscreen. They removed the tape rapidly, along with a thin layer of skin, and repeated this process for a number of times until they were able to remove the majority of the outer skin layer. The team used this to measure how deep the chemicals had penetrated into the skin, and found that traces of the conventional sunscreen chemical were found to have soaked deep within the skin. On the other hand, the team’s sunblock came off entirely with the initial tape strips. It was also discovered that a substantial amount of the new kind of sunscreen remained on the skin’s surface for days, even after exposure to water. It was only entirely removed when wiped repeatedly with a towel, proving the sunscreen’s efficacy.

In recent years, concerns have been raised about the safety of using sunblock. Earlier studies have indicated that commercial sunscreen may be doing harm than good as traces of its chemicals are found in users’ bloodstreams, urine and breast milk. These chemicals, according to previous research, cause disruptions with the endocrine system, such as blocking sex hormone receptors.

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