From: Andy Soos, ENN
Published April 8, 2010 04:41 PM

Sun Screen Nano Particles

Scientists are reporting that particle size may affect the toxicity of zinc oxide, a material widely used in sunscreens. Particles smaller than 100 nanometers are reported as slightly more toxic to colon cells than conventional zinc oxide when ingested. Their study is in the ACS Chemical Research in Toxicology, a monthly journal. Zinc Oxide is used in sunscreens as an effective agent to reduce and prevent sun burns. Part of its effectiveness is due to its particle size.


The report notes notes that there is ongoing concern about the potential toxicity of nanoparticles of various materials, which may have different physical and chemical properties than larger particles. Barely 1/50,000 the width of a human hair, nanoparticles are used in foods, cosmetics and other consumer products.

Nanotoxicology is the study of the toxicity of nanomaterials. Because of quantum size effects and large surface area, nanomaterials have unique properties compared with their larger counterparts.

Nanotoxicology is a branch of bionanoscience which deals with the study and application of toxicity of nanomaterials. Nanomaterials, even when made of inert elements like gold, become highly active at nanometer dimensions. Nanotoxicological studies are intended to determine whether and to what extent these properties may pose a threat to the environment and to human beings.

Some sunscreens do contain nanoparticles of zinc oxide. "Unintended exposure to nano-sized zinc oxide from children accidentally eating sunscreen products is a typical public concern, motivating the study of the effects of nanomaterials in the colon," the scientists note.

Some sunscreens do contain zinc oxide nanoparticles but not in a pure form. The advantage of sunscreen is that it prevents sunburns (skin damage) and long term sunscreen use may minimize potential skin melanoma from too much sun exposure.

The experiments with cell cultures of colon cells compared the effects of zinc oxide nanoparticles to zinc oxide sold as a conventional powder. They found that the nanoparticles were twice as toxic to the cells as the larger (non-nano) particles.

Although the nominal particle size was 1,000 times larger, the conventional zinc oxide contained a wide range of particle sizes and included material small enough to be considered as nanoparticles. The concentration of nanoparticles that was toxic to the colon cells was equivalent to eating 2 grams of sunscreen which is about 0.1 ounce. This study used isolated cells to study biochemical effects and did not consider the cumulative changes to these particles during passage through the digestive tract. The scientists say that further research should be done to determine whether zinc nanoparticle toxicity occurs in laboratory animals and people.

The study of nanoparticles and their benefits, effects, and toxicity is still in the beginning stages. As for the Zinc Oxide nanoparticles the current study exposed the colon cells directly to the nanoparticles as compared to the digested form. Much is still to be learned.

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