Interest in natural fibers such as cotton and wool is rising as people seek clothing that's safe and sustainable.

Some shoppers are turning away from synthetic fabrics, concerned that they contain potentially dangerous chemicals and shed microplastics, and as U.S. consumers show a desire for consumer products with safer ingredients.

Worldwide, the share of google searches for "100% cotton" roughly quadrupled over the past year from a year earlier, according to Google Trends data. At Urban Outfitters and Inditex's Zara brand, "cotton" appears in new-product names 30% and 28% more often than a year earlier, according to retail research firm Edited. On TikTok, influencers are showing off natural-fiber clothing "hauls" and promoting the garments' benefits.

"They're not chemically synthesized like synthetic fibers so they'll naturally biodegrade and can be returned to the earth," Summer Dean, who goes by Climate Diva on TikTok, told her followers last year, urging people to "check that fabric label."

But while natural fibers in many cases may use fewer chemicals than synthetics, a body of research is challenging whether they deserve a free pass.

Scientists are finding chemicals in cotton and other natural-fiber clothing that, in studies not specific to apparel, have been shown to penetrate skin and cause health effects at sufficient exposures. Natural-fiber garments also shed microfibers that have been found in oceans and human lung tissue, can persist in the environment and have harmed marine organisms in laboratory studies.

Yet natural fibers remain largely overlooked by scientists, and research on their prevalence, persistence and toxicity lags behind that of plastic fibers, says Thomas Stanton, a Loughborough University researcher who studies material pollution in water bodies.

"I have repeatedly come up against reviewers basically saying, 'natural fibers aren't an issue,' but with no evidence to say that," he says.

Host of chemicals

Textile manufacturers add chemicals to natural-fiber clothing to impart certain properties. These include PFAS-or perfluoroalkyl and polyfluoroalkyl substances-to repel water and stains, formaldehyde-releasing resins to resist wrinkles, biocides to control odor, silicone softeners and dyes.

Natural-fiber clothing also may contain chemicals that weren't added deliberately. Researchers have found hormone disrupters such as Bisphenol A-or BPA-in cotton-rich socks and phthalates in children's and infant's clothing. One study showed that cotton can pick up phthalates from indoor air more readily than polyester.

Whether a chemical in clothing poses a health risk to its wearer depends on how much is present, how readily it can migrate from fabric and penetrate skin, how much skin the garment touches and for how long, how much is absorbed and what levels are considered safe, says Awat Dostberg, a textile-chemicals researcher at Stockholm University.

In 2022, Miriam Diamond-an environmental chemist and University of Toronto professor-found that 100% cotton school uniforms contained the highest PFAS levels among the cotton and synthetic-blended uniforms she tested in the U.S. and Canada.

"We came to understand that higher levels of PFAS for stain repellency have to be added to a natural fiber like cotton relative to polyester because cotton takes up water so easily," says Diamond.

Research on chemicals in clothing is scant and no ordinary clothing has been shown to cause systemic illness in consumers. From studying PFAS in general, however, scientists know that some can migrate into sweat or potentially be inhaled. Elevated exposure to PFAS-which are used in many consumer products and can accumulate in the environment-has been linked to health problems such as high cholesterol, a decreased immune response to vaccines and an increased risk of kidney cancer.

Some countries, as well as U.S. states such as California and New York, have started to restrict PFAS in consumer clothing. And while textile makers are increasingly replacing PFAS with other water-repellent coatings, there is no guarantee the alternatives will be safer, says Petr Valenta, an expert in chemical hazard assessment at bluesign, a Swiss textile-standards company. "You fix one thing and you break another," he says.

As research continues to evolve, so do chemical formulations and testing protocols across the textile supply chain, says Mary Ankeny, head of product development at Cotton Inc., which represents the U.S. cotton industry. Continued progress toward safer alternatives and more transparency is important, she adds.

Some research suggests that cotton clothing contains fewer chemicals than synthetics.

When Dostberg recently examined children's garments sold in Sweden, he detected the highest number and levels of chemicals in garments made of 100% polyester, and the fewest and lowest levels in white and light-colored cotton. He found that many of the chemical residues in cotton and cotton-rich garments can wash out during laundering, but also that chemicals can migrate more readily from cotton than polyester into sweat.

He advises washing new clothes before wearing them, separately so chemicals don't migrate into other clothes. He also recommends white cotton for clothing worn directly against the skin, but cautions that research into cotton dyes is in its infancy.

Anti-odor is another increasingly common claim found on clothing labels, says Rebecca Fuoco, director of science communications at the nonprofit Green Science Policy Institute. Such clothing contains antimicrobial coatings to suppress odor-causing bacteria. These include silver-based compounds, quaternary ammonium compounds-or QACs-and zinc-based chemicals. Some enter wastewater during washing.

"Because their whole function is killing bacteria, they contribute to the broader antimicrobial-resistance crisis, where bacteria are becoming resistant to antibiotic drugs," says Fuoco.

She is particularly worried about QACs, some of which have been linked to skin irritation and asthma in people, while animal studies have raised concerns about fertility and fetal development.

Shoppers often can't tell from clothing labels what chemicals a garment contains. Brooks Brothers, for instance, describes its Supima cotton T-shirts as finished "to resist odors" without specifying the antimicrobial used.

A spokeswoman for Brooks Brothers said the brand's products follow "the highest safety standards and comply with U.S. and international laws and regulations."

Then there are dyes. Synthetic indigo, commonly used to dye bluejeans, can contain aniline, a manufacturing impurity that can slowly leach from clothing and penetrate skin, says Valenta. The World Health Organization classifies aniline as "probably carcinogenic" to humans, though human health effects from the amounts present in clothing haven't been established. Some wool dyes, meanwhile, contain chromium and copper, which can trigger allergic reactions, says Valenta.

Consumers seeking to reduce exposure to textile chemicals can check labels for OEKO-TEX Standard 100, which tests textiles against limits for harmful substances, or GOTS (Global Organic Textile Standard), which restricts chemicals used during textile processing. Bluesign recently launched bluepass, another certification covering chemicals and manufacturing processes.

Microfibers that can persist

Natural fibers don't shed microplastics but they do shed microfibers during washing, drying and everyday wear. Some of those microfibers may persist in the environment.

In a study of 916 seawater samples from six ocean basins, nearly 80% of identifiable fibers were cellulosic-including cotton-another 12% were wool or silk and just 8% were synthetic.

Peter Ryan, one of the authors, says the high proportion partly reflects the long history of natural-fiber use. "It's had enough time to spread all around the planet."

How fast natural fibers biodegrade depends on conditions including oxygen, temperature and light. A 2026 study found cotton and wool fibers preserved in layers of sediment from an English lake dating back as far as the late 19th century.

Jesse Daystar, Cotton Inc.'s chief sustainability officer, says "finding a fiber does not by itself tell us its impact." He points to research estimating the environmental impact of cellulosic microfibers as one to two orders of magnitude lower than that of synthetic fibers, largely because they degrade faster.

"Our research found that even with common dyes and finishes, cotton remained biodegradable and, on average, biodegraded faster than an oak leaf under the same conditions," he says.

Rodrigo Brasil Choueri, an associate professor and marine ecotoxicologist at the Federal University of São Paulo in Brazil, has been researching the impact of microfibers on marine organisms. He recently found that cotton, organic cotton and polyester microfibers caused cellular and DNA damage in mangrove oysters. He also contributed to a 2024 study that found that cotton and polyester microfibers disrupted the development of sea urchin embryos. "The thing we are calling attention to is that cotton microfibers are not inert," he says.

What this means for people is unclear. Microfibers can be ingested through food or water but also inhaled. Cotton fibers have been found in human lungs, but research on their prevalence and effects is limited.

Researchers say the answer isn't simply to swap one fiber for another, but to study and reduce impacts across textiles.

"If the public isn't aware that natural textile fibers in their clothing could potentially be a problem, then there isn't the same push that there has been for specific funding within the plastic pollution problem," Stanton says.

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