Smartwatches and fitness trackers may inadvertently expose wearers to harmful substances known as “forever chemicals”, according to a new study.

Researchers found that wristbands made from more expensive materials, particularly fluorinated synthetic rubber, contain significant levels of a type of forever chemical that could be harmful for human health.

This chemical, called perfluorohexanoic acid, or PFHxA, is a type of substance known as PFAS, which are found in a range of household items and have been linked to health issues.

PFAS are a group of chemicals prized for their water, sweat and oil-repellent properties, leading to their widespread use in consumer goods, from fitness wear to stain-resistant fabrics. However, their durability and resistance to breakdown in the environment have raised alarms over potential health risks.

“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,” said Graham Peaslee, University of Notre Dame professor and the lead author of the study.

The study, published in Environmental Science & Technology Letters on Wednesday, examined 22 smartwatch and fitness tracker wristbands, analysing their fluorine content as an indicator of PFAS presence.

Researchers found all 13 wristbands advertised as being made from fluoroelastomers, a synthetic rubber known for its durability, contain detectable levels of fluorine.

Alarmingly, two bands not advertised as such show traces of the chemical as well, indicating a broader problem of contamination.

The study found that wristbands costing more than $30 (£24) are particularly likely to contain higher levels of fluorine compared to cheaper ones, with concentrations of PFHxA exceeding 16,000 parts per billion in some cases. Previous studies by comparison have found PFAS concentrations in cosmetics to average around 200 ppb. “We have never seen extractable concentrations in the part-per-million range for any wearable consumer product applied to the skin,” Mr Peaslee said.

PFHxA is thought to be introduced during the manufacturing process as a surfactant but little is currently known about how easily the chemical is absorbed through the skin or the potential health effects of prolonged exposure. Recent research suggests that significant quantities of PFHxA can penetrate human skin under normal conditions, but further studies are required to confirm these findings.

Alyssa Wicks, lead author of the latest study, urged consumers to consider alternatives to bands with fluoroelastomer, recommending silicone as a safer, more affordable option.

“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,” she said.

PFAS have long been a topic of regulatory and scientific scrutiny due to their persistence in the environment and potential health risks.

In the US, only six PFAS compounds currently have federally defined exposure limits in drinking water while exposure through other sources, such as wearable products, remains an area of active research.

The authors of the study, funded by the University of Notre Dame, call for greater transparency from manufacturers about the materials used in wearable tech.

They also stress the need for further investigation into the potential health implications of long-term exposure to PFAS through skin contact.