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To understand behavioral changes, the researchers compared blood measurements with interviews with the women in which they were asked about nine behaviors that may lead to higher PFAS exposures, according to a news release. They also tested the presence of chemical markers of PFAS in six different dental flosses.

“In addition to specialized industrial applications and use in fire-fighting foams, PFASs are frequently used in consumer products,” according to the research. “Most commonly, they are used in nonstick and water-, stain-, or grease-resistant coatings, which are applied to a diverse range of products, including food packaging, cookware, carpet, furniture, textiles, and outdoor performance gear.” PFAS tend to be detected in water, soil and in American bodies thanks to their “extensive use and persistent nature.”

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The findings

According to the study, women who flossed with a particular dental floss — Oral-B Glide — had higher levels of the PFAS perfluorohexanesulfonic acid (PFHxS) compared to women who did not. The National Institutes of Health notes PFHxS has been previously linked to high cholesterol and altered thyroid function.

To further analyze the finding, researchers tested for fluorine (a PFAS chemical marker) in 18 different flosses using a technique called particle-induced gamma-ray emission spectroscopy.

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When they did so, the three Glide products examined tested positive. Two similar store-brand products marketed as comparable to Oral-B Glide, plus another marketed with “single strand Teflon fiber” also tested positive for fluorine.

Previous reports have highlighted Glide's use of Teflon-like compounds. Teflon is the brand name of PFAS polytetrafluoroethylene, which the Environmental Working Group has warned against using via dental floss due to risks of cancers, hormone disruption, brain and liver problems, as well as low birth weights.

In an emailed statement to The Atlanta Journal-Constitution Thursday, Procter & Gamble, maker of Crest and Oral-B floss said: "We have confirmed none of the substances in the report are used in our dental floss. The safety of the people who use our products is our top priority. Our dental floss undergoes thorough safety testing and we stand behind the safety of all our products."

It's possible participants may have been exposed to PFAS chemicals from other sources not included in the research or such as swallowing contaminated dirt, eating seafood from contaminated water. While study author Katie Boronow acknowledged this in a statement to INSIDER, researchers reiterated the study is based on self-reported use, including the effects of floss.

This is the first study to find “evidence that flossing with PTFE-based dental floss could contribute to an individual’s body burden of PFASs, but additional data are required to verify this finding,” researchers wrote.

The general hygiene lesson: You may want to avoid dental floss with PFAS, Boronow said in a statement.

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In addition to the floss findings, researchers noticed higher PFAS levels when participants:

had stain-resistant carpet or furniture

lived in a city with a PFAS-contaminated drinking water supply

ate food prepared in coated cardboard containers (African American women in particular)

Authors also noted that in this particular study, “African Americans ate French fries more often than non-Hispanic whites, so we infer that they may also consume more fast food such as hamburgers, which are sold in paper wrappers.” Fluorinated chemicals are frequently detected in fast food packaging.

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A potential limitation, according to the study, is that there are other behaviors that may contribute to PFAS exposure the researchers didn’t measure. This is why any racial differences regarding PFAS chemicals were left unexplained. Another limitation: the number and location of participants. But authors report figures were comparable with a nationally representative sample.

Future work should dive into Hispanic and Asian Americans as race differences may help identify “major exposure pathways,” according to the study.

Though PFSA environmental contamination via drinking water, for example, is considered a major public health threat most consumers can’t do much about, “this study strengthens the evidence that consumer products are [also] an important source of PFAS exposure,” Boronow said. “Restricting these chemicals from products should be a priority to reduce levels in people's bodies.”

Read the full study at nature.com.