You wear them at work, you wear them at play, you wear them to relax. You may even get sweaty in them at the gym.

But an investigation into headphones has found every single pair tested contained substances hazardous to human health, including chemicals that can cause cancer, neurodevelopmental problems and the feminisation of males.

Even products by market-leading brands such as Bose, Panasonic, Samsung and Sennheiser were found to contain harmful chemicals in the formulation of the plastics from which they are made.

Campaigners condemned “a market-wide failure” as they called for broad bans on whole classes of endocrine-disrupting chemicals in consumer goods and greater transparency from manufacturers about what is in their products.

“These chemicals are not just additives; they may be migrating from the headphones into our body,” said Karolína Brabcová, chemical expert at Arnika, part of the ToxFree LIFE for All project, a partnership of central European civil society groups that carried out the research.

“Daily use – especially during exercise when heat and sweat are present – accelerates this migration directly to the skin.

“Although there is no immediate health risk, the long-term exposures – especially for vulnerable groups like teenagers – is of great concern. There is no ‘safe’ level for endocrine disruptors that mimic our natural hormones.”

Around the world, there is increasing concern over the potential impacts of contaminating ecosystems, animals and humans with synthetic chemicals, and fears they are linked to the global rise in rates of cancer, obesity and infertility.

Many chemicals that have become ubiquitous, such as bisphenols, phthalates and poly- and per-fluoroalkyl substances (Pfas) have subsequently been discovered to have drastic biological effects. Despite that, many continue to be used in the manufacture of consumer goods, with little public awareness of what they are and what they might be doing to people.

Researchers say that while individual doses from particular sources may be low, a “cocktail effect” of daily, multi-source exposure nevertheless poses potentially severe long-term risks to health.

Campaigners from the ToxFree project said they decided to investigate the presence of such chemicals in headphones because the devices had “transitioned from occasional accessories to essential tools”, worn by users for long periods.

Researchers bought 81 pairs of in-ear and over-ear headphones, either on the market in the Czech Republic, Slovakia, Hungary, Slovenia and Austria, or from the online marketplaces Shein and Temu, and took them for laboratory analysis, testing for a range of harmful chemicals.

“Hazardous substances were detected in every product tested,” they said.

Bisphenol A (BPA) appeared in 98% of samples, and its substitute, bisphenol S (BPS), was found in more than three-quarters. Synthetic chemicals used to stiffen plastic, BPA and BPS mimic the action of oestrogen inside organisms, causing a range of adverse effects including the feminisation of males, early onset puberty in girls, and cancer. Previous studies have shown that bisphenols can migrate from synthetic materials into sweat, and that they can be absorbed through the skin.

“Given the prolonged skin contact associated with headphone use, dermal exposure represents a relevant pathway, and it is reasonable to assume that similar migration of BPA and its substitutes may occur from headphone components directly to the user’s skin,” the researchers said.

Also found in the headphones tested were phthalates, potent reproductive toxins that can impair fertility; chlorinated paraffins, which have been linked to liver and kidney damage; and brominated and organophosphate flame retardants, which have similar endocrine disrupting properties to bisphenols. Most were, however, found in only trace quantities.

The headphones investigation is the third undertaken by the ToxFree project. Previous investigations found bisphenol A, a known hormone disruptor, in baby dummies, including some labelled BPA-free, and that one in three pairs of women’s underpants contained toxic chemicals.

Bose, Panasonic, Samsung and Sennheiser did not respond to requests for comment.