We may earn a commission from links on this page.A recent study found that some smartwatch bands contain perfluorohexanoic acid, one of the forever chemicals that is suspected of contributing to health issues. But these chemicals, also called PFAS, arent in all watch bandsso heres how to know what youre buying.What did the recent study find?Before we get into the specifics of watch-band shopping, lets put this into context. The study found that perfluorohexanoic acid and other PFAS were present in many of the watch bands tested. The researchers did not look for health effects on the people who wore the watch bands.They tested 22 watch bands of various brands and price points and found that 15 of them contained more than 1% fluorine, which suggests that they contain PFAS. This included all 13 of the bands that were advertised as being made with fluoroelastomersmore about that in a minute, since this is a term youll want to pay attention to when shopping.The researchers were able to extract a specific PFAS chemical, perfluorohexanoic acid, from several of the bands. Other research has shown that this chemical can be absorbed through the skin, so it may be worth avoiding until we know more about its health effects.How dangerous are PFAS in watch bands?The short answer is: We dont know. The Environmental Protection Agencys fact sheet on PFAS explains that exposure to certain levels of PFAS has been linked to health issues such as reduced fertility, increased risk of cancer, developmental delays in children, and reduced immune system response to vaccines, to name a few.But thats a summary of a broad area of research: Some exposures that have been studied involved very high levels of the chemicals (for example, in people who work with large amounts of them). There are also many different chemicals in the PFAS family and some may be more concerning than others.The EPA writes: Research is also underway to better understand the health effects associated with low levels of exposure to PFAS over long periods of time. In short, we dont know a lot yet about the health effects of PFAS in watch bands, or in other sources like water and soil. But it may be a good idea to avoid bands with PFAS if you want to be cautious.Graham Peaslee, who led the study on watch bands, points out that the chemical the study focused onperfluorohexanoic acid, one type of PFASis under-studied because until recently, researchers didnt realize it accumulated in the blood. (It can be found in whole blood, but not in the blood serum that is usually sampled for these types of studies.) More studies on the health effects will hopefully come out in the future.Which watch bands contain PFAS?The bands that were tested included ones from Nike, Apple, and Fitbit, but the study didnt call out specific brands or items as testing positive. Peaslee told me in an email that We didn't test enough samples to be sure any one brand is entirely PFAS free, or entirely PFAS. So you cant rely on brand names.What you can look for is the material that the watch band is supposed to be made of. Remember when I said that all the fluoroelastomer bands in the study appeared to contain PFAS? Fluoroelastomer is a type of synthetic rubber that is supposed to be nicer quality than silicone watch bands, so manufacturers often proudly say that these bands are made of fluoroelastomer or FKM rubber. Peaslee says: If [a watch bands description] says fluoroelastomer or FKM, I would avoid it, but if it says silicone, nylon, or other fabric, leather, or metal, then you are PFAS-free.What is the difference between fluoroelastomer and silicone watch bands?Silicone watch bands are not known or suspected to contain PFAS. Fluoroelastomer bands, on the other hand, are more likely to contain PFAS based on the results of this recent study.Fluoroelastomers are used in higher-end watch bands because they are more resistant to damage from sweat, oils, and chemicals. They have a less sticky or dusty texture than silicone. Many people prefer them, and they are generally more expensive than silicone bands. Peaslee says if youre paying more than $30 for a rubbery-looking band, its likely to be fluoroelastomer. (In the study, none of the bands under $15 tested positive for PFAS. This is one place where it pays to be cheap.)Fluoroelastomer bands are often advertised as being made of FKM rubber, like this one that says in the product description: FKM Rubber (Not Silicone).What should you look for when buying a band for your smartwatch or fitness tracker?Not all watch bands tell you what they are made of; some of the bands in the study werent advertised as being fluoroelastomer, but contained fluorine anyway.Based on this study and Peaslees advice, you stand the best chance of avoiding PFAS in a watch band by looking for these features:Not labeled as fluoroelastomer or FKMLabeled as being made of a different, specific material, like silicone, nylon, or leatherInexpensive (under $30; ideally under $15)I asked Peaslee about banned substances lists that have been released by some manufacturers, like this one from Garmin and this one from Apple. He said that since 2016, manufacturers have been making an effort to remove PFOA and PFOS (two types of PFAS) from their products. But there are still plenty of other PFAS besides those, so the existence of those lists doesnt tell you that a brand is safe.Peaslee hopes that with enough pressure from consumers, brands will start marketing products as PFAS-free. But for now, the rules of thumb above are your best bet for finding a watch band that doesnt contain PFAS.