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Summer is upon us full force. For many that means a lot of time outside, preferably at the beach. Our largest organ, our skin, doesn’t do well with too much sun exposure and the “too much” part is pretty fuzzy. Generally, by the time we feel uncomfortable in the sun, it’s already too late. To prevent sun damage, we slather on sunscreen. But oops, the ingredients in most commercial sunblocks don’t just stay on the skin’s surface, and that’s a problem.

The particles in most sunscreens are small enough to pass through our skin’s layers and enter the blood stream. According to scientists and researchers at Yale Medical School who have developed a sunblock that doesn’t penetrate the skin, those that do leave traces of their chemicals in users bloodstream, urine, and breast milk. They cite evidence that “these chemicals cause disruptions with the endocrine system such as blocking hormone receptors.” In some cases changes due to ultraviolet light before the chemicals are absorbed can cause cellular damage and possibly even skin cancer.

There are commercially available sunblocks with particles large enough that they don’t penetrate the skin. You’ve probably seen them on lifeguard and skier noses. Zinc oxide and titanium dioxide stay on the skin surface and do a great job blocking the sun, but because of the way they look most people don’t and wouldn’t use them as a general purpose sun block.

Working with bioadhesive nanoparticles, the Yale scientists developed a sunblock that is clear but doesn’t penetrate the skin. In testing with mice, the sunscreen never went beyond the surface layer of the skin. Even with repeating washing, it stayed on the skin until wiped off with a towel, at which point it was completely removed. They used the nanoparticles to “encase” padimate O, an effective and common sunscreen ingredient, with the effect that the transparent mixture protected but did not penetrate the skin. Testing with humans has yet to begin, so we won’t see it on the market this summer, but perhaps next summer and beyond we’ll be able to use a protective sunscreen that stays out of our bloodstream.