Yanna Lee

Sunscreen may get safer and more effective, thanks to Yale researchers.

The researchers from the biomedical engineering department created sunscreens composed of nanoparticles with bioadhesive properties. Most sunscreens on the market are partially absorbed into the body through the skin, which poses certain health risks including cancer, according to study co-author Yang Deng, researcher alumnus from the department of biomedical engineering. But Yale researchers found that the nanoparticles with bioadhesive properties remained on the skin, both improving the efficacy of sunscreen particles and inhibiting their absorption into the skin. Unlike most current sunscreens, the particles of the new sunscreen could very easily be removed from skin through active towel drying, Deng added. Because of this difference, using the bioadhesive nanoparticles made sunscreens safer and better at preventing damage from the sun, Deng said.

“Our nanoparticle sunblock formulation can provide just as effective [ultraviolet] protection when compared to commercial sunscreen, with the added benefit of preventing ROS-mediated cellular toxicity,” co-author Asiri Ediriwickrema MED ’14 said in a Sunday email to the News. “The fact that our particles do not penetrate the skin is key in preventing these toxicities.”

Although sunscreen has several benefits, such as preventing skin from burning on sunny days, it is not without its downsides, the researchers said. Many commercial sunscreens’ active ingredients work by absorbing ultraviolet rays, preventing the rays from reaching the skin, according to the study paper. But many particles of active ingredients are small enough that they may be absorbed into the skin, potentially disrupting the body’s systems, according to the paper.

Some sunscreens, like those that include titanium dioxide or zinc oxide, have larger particles that sit on top of the skin, minimizing absorption. However, these tend to look semi-opaque once applied, giving skin a chalky, white layer that some might find unappealing, according to Michael Girardi MED ’92, one of the authors of the paper and a professor at the Yale School of Medicine.

Additionally, the organic filters used in commercial sunscreens have posed health concerns for years, Deng said. They can penetrate skin and reach the bloodstream, causing direct cellular toxicity and systemic side effects, according to Deng. For instance, several UV filters have been detected in human urine and breast milk samples after topical treatment, and may bring about systemic effects including endocrine disruption, he added.

The combination of UV light and sunscreen can form reactive oxygen species in skin, and may cause significant damage in the cells, according to Girardi. Researchers used pig skin to test the penetration of UV filters of sunscreens using different formulations and two mice models to demonstrate the unique properties of their sunblock, Deng said. He noted that pig skin was a reasonable substitute for human skin in penetration studies, and that it has been previously examined in a variety of topical applications, including penetration studies from chemicals and nanoparticles. The absorption of sunscreen into skin was dramatically reduced when bioadhesive nanoparticles were used in sunscreen formulations, Eridiwickrema said.

“Developing safe and effective therapies using nanotechnology is a primary focus of the Saltzman Lab,” said Eridiwickrema. “We realized that the particles we were engineering could provide effective topical therapies and so we decided to explore those ideas.”

Deng added that they had originally designed the particles to attach to ligands — a molecule that bonds to another larger molecule for targeted delivery, but they found that the particles have excellent adhesion properties. They then decided to use the particles for topical applications, like sunscreens.

Bioadhesive nanoparticles like these could lead to changes in sun-protective products. Deng said that the bioadhesive nanoparticles will likely be incorporated into commercial sunscreens within the next few years.

The study was published on Sept. 28 in the journal “Nature.”