THE DETAILS: The authors of this new study were trying to demonstrate what might happen if someone were to ingest nanoparticles orally, either in an occupational setting or by licking sunscreen off their lips or face. So they exposed mammal colon cells to various-sized particles of zinc oxide, a mineral used in sunscreens that physically blocks UV rays from skin rather than absorbing them and converting them to heat, as chemical sunscreen ingredients do. They found that nano-sized zinc oxide particles were twice as toxic to the cells as larger particles.
WHAT IT MEANS: If you were to ingest zinc oxide nanoparticles orally, there's a chance that they could cause damage to your colon and intestinal walls. "There have been some concerns about different nanomaterials, and zinc happens to be one that can be quite toxic if it comes into contact with cells," says the study's lead author Philip Moos, assistant professor in pharmacology and toxicology at the University of Utah. But exactly how much damage isn't really clear. On the one hand, he says, your stomach acid can break zinc oxide down into zinc particles, and your stomach and intestines have mechanisms that prevent the absorption of metals like zinc into the body. On the other hand, if you ingest large quantities, the zinc particles you consume may combine with the zinc already in your system, he says, and it might overload your body's ability to get rid of it.
The bottom line? Zinc oxide nanoparticles have the potential to cause harm, but you can still find sunscreens that use non-nano-sized zinc oxide or another mineral called titanium dioxide and still protect against sun damage without bothering your intestines. "Using sunscreen is a good idea regardless," says Moos, but he adds that some studies have found that titanium dioxide can penetrate cells more easily than zinc oxide, so he opts for the latter. And, he says, the evidence is stronger against sunscreens ingredients such as oxybenzone, avobenzone, and benzophenone, which have been found repeatedly to interfere with hormones. "Personally, in my own family we use zinc oxide sunscreen because we think it's the safest sunscreen that's available," he says.
Moss says that his results shouldn't be particularly concerning to adults, who have larger bodies that are better able to cope with contaminants. "This is more of a pediatric concern," he notes. Opt for nanoparticle-free sunscreens on kids, who have a tendency to stick sunscreen-covered hands in their mouths, and while you're at it, look for adult lip balms free of nanoparticles so you won't end up with any in your mouth (or gut).
To keep nanoparticles out of your beach bag this summer, take a second to read labels and find safer lip balms and baby sunscreens:
• Cover your lips. It's very easy to get skin cancer on your lips, so you shouldn't forget them. And don't replace an SPF lip balm with ordinary lip gloss; a study published last year found that lip glosses can actually increase the risk of cancer because they allow more UV rays to penetrate skin than if your lips were left unprotected.
• Watch what you lick. Every year, the Environmental Working Group (EWG) digs up safer sunscreens that are free of nanoparticles and tests them for efficacy. Their picks for lip balms this year include:
UV Natural Lip Screen SPF 30+
UV Natural Sport Lip Screen 30+
Badger SPF 15 Sunscreen Lip Balm Unscented
Purple Prairie Botanicals Sunstuff Lip Balm, SPF 30
• Keep kids covered. The American Academy of Pediatrics recommends avoiding the use of sunscreens on kids under 6 months of age. Instead, young infants should be kept in the shade or inside to prevent overheating. For other tots inclined to lick their hands or face, try these safer sunscreens (these are also good for adults with sensitive skin):
California Baby Sunblock Stick No Fragrance, SPF 30+
Thinkbaby Sunscreen, SPF 30+
UV Natural Baby Sunscreen, SPF 30+
Caribbean Solutions Sol Kid Kare Natural Sunscreen, SPF 25