There have been many concerns over the safety of sunscreen, particularly the use of nanoparticles, and this new development from Yale, published in the online edition of the journal Nature Materials, claims it may have found a solution – a sunscreen that stays on the surface of the skin.
“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,” says the paper’s senior author, Mark Saltzman, the Goizueta Foundation Professor of Biomedical Engineering.
“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.”
To make their sunscreen, the researchers developed a nanoparticle with a surface coating rich in aldehyde groups, which stick to the outer skin layer, so the nanoparticle’s hydrophilic layer essentially locks in the active ingredient, a hydrophobic chemical called padimate O.
Some sunscreen solutions that use larger particles of inorganic compounds, such as titanium dioxide or zinc oxide, also don’t penetrate the skin; however these are often quite thick on the skin, almost opaque, and so for aesthetic reasons aren’t very popular.
In their study, the Yale team says that by using a nanoparticle to encase padimate O, an organic chemical used in many commercial sunscreens, its sunscreen is both transparent and stays out of the skin cells and bloodstream.
Testing their sunscreen against ultraviolet rays, the team found that even though it used a significantly smaller amount of the active ingredient compared to commercial sunscreens, their formulation protected equally well against sunburn.
They also looked at an indirect effect of UV light, stating that when the active ingredients of sunscreen absorb UV light, a chemical change triggers the generation of reactive oxygen species (ROS).
The team explains that if a sunscreen’s agents penetrate the skin; this chemical change could cause cellular damage, and potentially facilitate skin cancer.
Tests of the Yale team’s sunscreen’s penetration levels were shown not to penetrate the skin.
Other tests also showed that a substantial amount of the sunscreen remained on the skin’s surface for days, even after exposure to water. When wiped repeatedly with a towel, the new sunblock was entirely removed.