What’s the best sunscreen? It’s a question that troubles beachgoers, athletes, and scientists alike.

Mark Saltzman, who falls into the last category, was so concerned by the time his third child was born that he wanted to engineer a better sunblock. “The initial goal … was to make a sunblock that lasted longer,” says Saltzman, a biomedical engineer at Yale University.

“But as I read more about sunscreen, I became aware of people’s concerns about safety.” Now, he and his colleagues have unveiled the results of their research: a nanoparticle-based sunblock, which they say is longer lasting and less likely to leak into the body than traditional sunscreen.