Non-penetrating nano sunscreen created at Yale

University researchers create new sun block

While few people would question the necessity of sunscreens, concerns about the use of nanotechnology and chemicals in formulations are growing. Researchers at the University of Yale may have found a potential solution in a nano-technology formula that doesn't penetrate the skin.

The new ingredient, made from bioadhesive nanoparticles, is designed to remain on the surface of the skin, rather than penetrating it. The researchers work was published in the 28 September issue of Nature Materials. The nanoparticles have a surface coating rich in aldehyde groups, which stick to the outer skin later. The layer locks in the active ingredient – a hydrophobic chemical called padimate O.

Mark Saltzman, senior author of the paper and Goizueta Foundation Professor of Biomedical Engineering, explained: "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.'

The sunblock's efficacy was tested against ultraviolet rays and it was found to protect equally well as commercial sunscreens, despite using a significantly smaller amount of active ingredient.

The researchers also looked at the indirect effects of UV light. When active ingredients of sunscreen absorb UV light, a chemical change can trigger the generation of oxygen-carrying molecules, known as reactive oxygen species. This chemical change can cause cellular damage and potentially facilitate skin cancer if the active ingredient penetrates the skin.

Michael Girardi, co-author of the study and Professor of Dermatology at Yale Medical School, said: "Commercial chemical sunblock is protective against the direct hazards of ultraviolet damage of DNA, but might not be against the indirect ones. In fact, the indirect damage was worse when we used the commercial sunblock."

Some sunscreens use larger particles of titanium dioxide or zinc oxide which do not penetrate the skin. However, many consumers dislike these products due to their opaque appearance on the skin. The new Yale formula is both non-penetrating and transparent.

To test penetration levels of the new formula, the researchers applied strips of adhesive tape to skin previously treated with sunscreen. The tape was then removed rapidly, along with a thin layer of skin. Repeating this process allowed the researchers to remove the majority of the outer layer of skin and measure how deeply the chemicals had penetrated it.

While traditional sunscreens were found to have soaked deep within the skin, the Yale team's new sunblock came off entirely within the initial tape strips. Despite this, a substantial amount of the team's sunblock remained on the skin's surface for several days, even after exposure to water. After wiping with a towel, it was entirely removed.

Girardi specialises in skin cancer development and said that limited research has been undertaken into the effects of sunblock use and the generation of reactive oxygen species. Previous studies have identified traces of commercial sunscreen chemicals in user's bloodstreams, urine and breast milk.