Smartwatch bands may expose users to harmful forever chemicals

Smartwatches and fitness trackers have become ubiquitous forms of wearable tech, accompanying many people throughout their days (and nights). But they may expose the skin to so-called forever chemicals in the process. More expensive wristbands made from fluorinated synthetic rubber revealed particularly high amounts of one forever chemical, perfluorohexanoic acid (PFHxA), according to a study published in ACS' Environmental Science & Technology Letters.

This discovery stands out because of the very high concentrations of one type of forever chemical found in items that are in prolonged contact with our skin."

Graham Peaslee, corresponding author of the study

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that are very good at two things -; lasting seemingly forever in the environment and repelling water, sweat and oil. Because of the latter properties, manufacturers include these chemicals in many consumer products, such as stain-resistant bedding, menstrual products and fitness wear, including smartwatch and fitness tracker wristbands. The bands contain fluoroelastomers, synthetic rubbers made from chains of PFAS, to create a material that avoids discoloration and repels dirt. Though this durability makes the bands great for sweaty workouts, it might also present a source of these compounds to get under the wearer's skin -; literally. So, Peaslee and co-authors Alyssa Wicks and Heather Whitehead investigated several commercially available watchbands for the presence of fluorine as well as 20 individual PFAS. 

The team screened 22 wristbands from a range of brands and price points, most of them newly purchased but a few previously worn. All of the 13 bands advertised as being made from fluoroelastomers contained the element fluorine. But two of the nine bands that did not advertise being made from fluoroelastomers also contained fluorine, which indicates the potential presence of PFAS. Of those tested, wristbands that cost more than $30 contained more fluorine than those under $15. Next, following a chemical extraction, all the wristbands were checked for 20 different PFAS. PFHxA was found to be the most common, appearing in nine of 22 tested wristbands. The median PFHxA concentration was found to be nearly 800 parts per billion (ppb), and one sample exceeded 16,000 ppb. Comparatively, previous research by the team in 2023 on cosmetics found a median concentration of around 200 ppb of PFAS. Currently, only six PFAS have federally defined exposure limits for drinking water in the U.S.; exposure limits for other PFAS and other exposure routes are still being studied. 

"We have never seen extractable concentrations in the part-per-million range (>1000 ppb) for any wearable consumer product applied to the skin," says Peaslee. 

The researchers suggest that the large amounts of PFHxA found in the wristbands may be a result of the compound being used as a surfactant during the fluoroelastomer manufacturing process. Scientists do not currently understand how readily PFHxA transfers into the skin, nor the potential health effects it poses once it gets there, though Peaslee says recent studies suggest that a significant percentage could pass through human skin under normal conditions. 

Wicks, the study's lead author, says the team recommends purchasing lower-cost wristbands made from silicone. "If the consumer wishes to purchase a higher-priced band, we suggest that they read the product descriptions and avoid any that are listed as containing fluoroelastomers." 

The authors acknowledge funding from the University of Notre Dame.