Nanotechnology is widely used in sunscreen formulations.
Nanotechnology is particularly effective when formulating with inorganic pigments. The two most popular inorganic pigments used in sunscreens are titanium dioxide (TiO2) and zinc oxide (ZnO), both of them physically block the sun’s UV rays from touching the skin. They work well and enable the formulator to use less organic oils as chemical sunscreens. Although high sun protection factors (SPF) can be achieved with these combinations, traditional inorganic pigments leave a white film on the skin. But using nanoparticles of the two inorganics reduces the visibility of the whiteness.
However, TiO2 nanoparticles emit photoelectrons when exposed to UV light. These electrons then induce the formation of peroxides, free radicals and other reactive oxygen products that interact with lipids and DNA, which could lead to medical problems.
Evidence has been found that TiO2 nanoparticles catalyze DNA damage. But coating the particles with polymers apparently allows them to be used with less risk in cosmetic products.
Still, several years ago the Australian Food and Drug Administration noted, “There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these cells (photo-mutagenicity with zinc oxide).However, this would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells.The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer (stratum corneum) of the skin.”
In addition to sunscreens, TiO2 nanoparticles are used in toothpaste, eyeshadows and even paint.
Laboratory testing of nanoparticles continues. Last year, University of California at Los Angeles researchers gave drinking water with added TiO2 nanoparticles to laboratory mice. The mice began to show genetic damage by the fifth day of this exposure. Researchers theorize that the nanoparticles wander throughout the body causing oxidative stress which can result in cell death.They accumulate in different organs because there is no way to eliminate them internally, and since they are so small, they can go anywhere, even through cells to disrupt body functions on a sub-cellular level.
Another recent study, this one conducted by scientists at the University of Toledo in Ohio, consisted of exposing E. coli bacteria in laboratory cultures to various amounts of TiO2 nanoparticles. It was found that, when exposed to small concentrations of the nanoparticles for less than one hour, there were large reductions of survival rates of the bacteria.Another bacteria called P. putida, a beneficial soil microbe, could not tolerate silver, copper oxide and zinc oxide nanoparticles. This might indicate a danger for aquatic life. The particles get in the water by washing down the drain as people bathe and the bath water goes through municipal sewage plants and then into lakes or rivers where microorganisms serve essential roles in maintaining a healthy environment.Of course, if bath water removes nanoparticles from the body, then it would seem to prove that they do not penetrate the human skin.
At the present time, it has yet to be proved that nanoparticles can actually penetrate healthy skin and travel to reach the DNA. And even if they did, it is not known if the UV light could still reach the nanoparticles and lead to oxidative stress. Clearly, more research is still needed in the use of nanoparticles in personal care products.
Harvey Fishman has a consulting firm located at 34 Chicasaw Drive, Oakland, NJ 07436, firstname.lastname@example.org, specializing in cosmetic formulations and new product ideas, offering tested finished products. He has more than 30 years of experience and has been director of research at Bonat, Nestlé LeMur and Turner Hall. He welcomes descriptive literature from suppliers and bench chemists and others in the field.