Researchers have found toxic metals — including arsenic and lead — in over a dozen popular brands of tampons, raising questions about a menstrual hygiene product used by millions of Americans.

Their study, published last week in the scientific journal Environment International, adds to a growing body of research about chemicals found in tampons but is believed to be the first to specifically measure metals.

The negative health effects of heavy metals are well-documented and wide-ranging, including damaging the cardiovascular, nervous and endocrine systems; damaging the liver, kidneys and brain; increasing the risk of dementia and cancer and harming maternal health and fetal development.

“Despite this large potential for public health concern, very little research has been done to measure chemicals in tampons,” lead author Jenni Shearston, a postdoctoral scholar at the UC Berkeley School of Public Health, said in a statement.

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Shearston led a team of scientists from Columbia University and Michigan State University in examining 30 tampons from across 14 brands and 18 product lines, which they did not name in the study.

The sampling includes products of various absorbencies, listed as “top sellers” by a major online retailer and purchased both online and at stores in New York City, London and Athens between September 2022 and March 2023.

Researchers detected “measurable concentrations” of all 16 metals they were looking for in the tampons, as well as “elevated mean concentrations” of toxic metals including lead, arsenic and cadmium.

The study says there are several ways metals could get into tampons. Raw materials like cotton and rayon could be contaminated by water, air or soil during production, while metals may in some cases be added intentionally in the manufacturing process either for odor control, pigment or as an antibacterial agent.

The exact amount of metals varied among the tampons, based on which region they were purchased from, whether they were made of organic or non-organic material and on store- versus name-brands, according to the study.

“Lead concentrations were higher in non-organic tampons while arsenic was higher in organic tampons,” it added. “No category had consistently lower concentrations of all or most metals.”

Researchers say the study marks an important first step in confirming the presence of toxic metals in tampons, which are used by an estimated 52% to 86% of menstruating people in the U.S.

But it doesn’t give them enough information to definitively link the metals to negative health effects.

They say more studies are needed to determine to what extent such metals might “leach out of tampons” and into peoples’ bodies. They’re calling not only for more research, but also for stronger regulations.

“I really hope that manufacturers are required to test their products for metals, especially for toxic metals,” Shearston said. “It would be exciting to see the public call for this, or to ask for better labeling on tampons and other menstrual products.”

In the U.S., the Food and Drug Administration (FDA) classifies tampons as medical devices and regulates their safety. However, there is no requirement to test tampons for chemical contaminants, and the FDA only recommends that tampons not contain pesticide residue or dioxin.

FDA spokesperson Amanda Hils told NPR that “all studies have limitations,” pointing to the outstanding questions about whether metals are released from tampons and into the bloodstream. Nevertheless, she said the agency is reviewing the research.

“We plan to evaluate the study closely, and take any action warranted to safeguard the health of consumers who use these products,” Hils added.

NPR has reached out to the industry Center for Baby and Adult Hygiene Products (BAHP) and its U.K. counterpart, the Absorbent Hygiene Product Manufacturers Association, for comment.

The BAHP defended the safety of its member companies’ menstrual products in a 2022 statement, acknowledging news coverage on the presence of chemicals and saying “if present, these are not intentionally added by the manufacturers.”

“Some of these impurities are present in the environment or naturally present at much higher levels in common fruits and vegetables or even made by the human body,” it said, adding that its members use “rigorous criteria for quality and hygiene.”

The bigger question: How harmful are these metals?

Several experts told NPR that they were not surprised by the researchers’ findings, since other studies over the years have detected potentially harmful chemicals in tampons and other menstrual products, including period underwear.

Catherine Roberts, a health and science journalist at Consumer Reports who has written about tampons, says it’s more surprising that the question wasn’t investigated sooner.

“It’s in the most sensitive part of people’s bodies. It’s so close to us,” she says. “We use so many [tampons] over a lifetime. It’s just wild to me that this is so both so little researched and so little regulated.”

People who menstruate may use more than 7,400 tampons over the course of their reproductive years, the study authors calculated, with each tampon staying in the vagina for several hours at a time.

Dr. Nathaniel DeNicola, an OB-GYN who served as the environmental health expert for the American College of Obstetricians and Gynecologists, says the more pressing question is not whether there are chemicals in tampons, but “when does it convert to a dangerous amount?”

Some of the metals found in the tampons — including copper, calcium, iron and zinc — are not only considered safe, but recommended for patients by many doctors, he notes. They would not be damaging in low amounts, but a cumulative amount could have a lasting effect on a person’s endocrine functions.

Trace amounts of arsenic, for example, are sometimes found in food and not considered to be toxic, but high amounts could be fatal. In contrast, as the study notes, “there is no safe exposure level” to lead.

It’s not clear from the study whether people are getting harmful amounts of each metal from tampons, DeNicola says.

“When you start to look at the kind of chemicals that are found in our human system, the reality is that in modern life, we’re kind of swimming in them,” he adds. “And it’s not to say that it’s nothing we should worry about. I mean, I don’t think most people hear that and think, ‘Oh, good, I’ve got more plastic in me.’ But we do have to recognize that small amounts of these chemicals are ubiquitous.”

What to do if you’re worried

To Roberts, one of the main takeaways from the study is that the “organic label was clearly not a guarantee that these products would not have heavy metals.” So what are concerned shoppers supposed to do?

Ideally, she says, regulators would mandate heavy-metal testing for tampons to take some of the pressure off consumers.

Until then, she says, there are some measures that tampon users can take to try to reduce their exposure to chemicals in general.

Those include choosing products that don’t contain plastic (including polyester and polypropylene) and avoiding those with fragrances and colorants.

“Something that people who look at this tend to say is that you want to look for period product labels that have fewer and simpler ingredients,” Roberts adds.

DeNicola recommends relying on a combination of “third-party testing and some personal due diligence.” He says there are apps shoppers can use to scan product barcodes and see what chemicals they contain, which could be useful for personal care and feminine hygiene products.

In some cases, people might want to consider alternatives to tampons, such as pads or menstrual cups. The reusable cups have become increasingly popular in recent years, especially given their lower environmental impact compared to tampons.

Some of the downsides of tampons were evident well before this study.

DeNicola notes that plastic from tampons is one of the biggest sources of waste worldwide (and that some brands are more eco-friendly than others). Roberts points out that even if they didn’t contain chemicals, tampons would still pose a risk of toxic shock syndrome, a rare but potentially life-threatening illness (wearers can reduce their risk by changing their tampons frequently).

But DeNicola stresses that this study doesn’t have him running to tell his patients not to use tampons at all.

“I don’t think we’ve established that risk yet,” he says. “I think it’s more of a reality check for the consumers and the public at large, that most products that you’re using do not go through rigorous testing for safety, and most products do have chemicals in there somewhere.”

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UC Berkeley Study Finds Toxic Metals in Popular Tampon Brands. Here's What Experts Advise