Thinx Denies Claims of Toxic Chemicals in Its Menstrual Underwear

"We take this [matter] very seriously," said a spokesperson for the brand

(Photo: Stocksy; Illustration: Maegan Fidelino)
(Photo: Stocksy; Illustration: Maegan Fidelino)

Update: Canadian company Knix announced on January 21 that “after pursuing extra third-party testing, their products are confirmed to be 100%, completely free of harmful chemicals and PFAS.” 

Menstrual underwear has become more and more popular over the past few years, especially among millennials who want more environmentally friendly and safer feminine products rather than single-use products like pads and tampons, both of which have been found to have toxic chemicals linked to cancer, reproductive harm, hormone disruption and allergic reactions. (For a full list of chemicals detected in period products, check out Women’s Voices of the Earth, an American environmental organization specializing in research and advocacy regarding toxic chemicals.) Oh, and let’s not forget about toxic shock syndrome (TSS), the potentially fatal condition caused by the release of toxins from an overgrowth of bacteria that’s sometimes associated with tampon use because the blood that accumulates in a tampon can serve as a breeding ground for said bacteria.

But it turns out that not all period-proof underwear is exactly safe. According to a report published in Sierra Club’s magazine, Sierra, popular menstrual-underwear brand Thinx reportedly has toxic chemicals in the crotch of some of its products. (As if 2020 hasn’t already given us enough horrible news.)

In the article, the story’s reporter, Jessian Choy, says she decided to mail unused Lunapads and Thinx menstrual underwear to Dr. Graham Peaslee, a nuclear scientist at the University of Notre Dame, to see if they contained toxic chemicals. Dr. Peaslee, as Choy notes, was responsible for discovering PFAS (that is, per- and polyfluoroalkyl substances) in fast-food wrappers in 2017. PFAS are a group of man-made chemicals commonly used in waterproofing and stain-resistant finishes that don’t break down and accumulate over time, both in the environment and in the human body. This means they can remain in the human body for long periods of time, which can result in adverse health effects, such as fertility issues and even cancer.

According to Dr. Peaslee’s results, Lunapads were free of PFAS but Thinx underwear—specifically the “organic” brief and “organic” BTWN Shorty underwear for teens—had high levels of PFAS, especially on the inside layers of the crotch.

As Choy notes, the vagina is a very absorbent and very sensitive part of the body. The permeable mucous membranes that line the vaginal tissues and protect the body from bacteria can also easily absorb chemicals without metabolizing them. So it’s safe to say that having harmful chemicals close to that area is not a great idea.

“Exposure to PFAS at even the lowest concentrations has been shown to harm human health,” Choy writes. “The crotch in my underwear had 3,264 parts per million (ppm), and the one for teens had 2,054 ppm… That’s high enough to suggest that they were intentionally manufactured with PFAS.”

In an email response to FLARE, however, Thinx shared lab test results from its latest product-safety evaluation in September 2019 and claimed they “found no PFAS chemicals were detected.”


“Our customers’ health and safety is our number one priority, and we will always work to deliver the safest products available,” said Maria Molland, CEO of Thinx Inc, in a statement to FLARE. “All Thinx and Thinx (BTWN) underwear undergo the most stringent product safety evaluations available. While Thinx products comply with all legal safety requirements in Europe and the United States, we strive to go beyond those requirements and are constantly working to improve our products and manufacturing processes to use the safest substances and materials available.”

Molland continued, “Thinx uses both OCS-certified and GOTS-certified organic cotton, and our product safety testing is conducted to meet the robust European safety standards of REACH and OEKO-TEX, which include testing for some PFAS chemicals. Based on these third-party tests, PFAS chemicals were not detected in Thinx products.”

Molland concluded by saying that Thinx is treating these claims “with the serious that it deserves” and “working to dramatically expand the list of chemicals that we test for in our products, including unregulated PFAS chemicals, and develop a robust safer chemicals policy across our entire family of brands.”

“If any of these chemicals are found, we will move swiftly to remove them from our products,” she concluded.

Following Sierra’s report, Twitter users were quick to ask Canadian company Knix if its menstrual underwear also contained the toxic chemicals.

In an emailed statement to FLARE, Knix founder and CEO, Joanna Griffiths, said, “At Knix, the core of our mission is to listen to women and deliver products that they truly want – and intimates that support their health are at the top of that list. When developing our patented leakproof technology, our emphasis was on technical features at the fiber and construction level – eliminating the potential risks involved with using topical treatments and chemical additives.”

She continued, “Our leakproof product assortment is Fluorocarbon-free meaning no PFOA and no PFOS. We also opted to avoid stain resistant features, and that was an intentional choice. The manufacturing of stain resistant products typically requires chemical additives, and their historical use has predominantly been in carpets, furniture and other products that are a far cry from underwear. To us – the possibility of a stain will always be far less of a concern than putting our customers’ wellbeing at risk.”

Griffiths concluded by saying despite Knix products not historically testing for PFAS, the company is currently pursuing testing for customer peace of mind.

“While we have years of extensive product and consumer safety testing, due to the information above we historically have not tested for PFAS. However, given the recent news in our category and for consumer peace of mind, we are currently pursuing this test and will have the results within ten days. As the category continues to grow, we would welcome regulation around consumer safety standards.”

According to a response posted on Knix’s Twitter account, the main difference between Knix and Thinx is that the former’s “patented technology takes place at the fiber level vs a chemical coating.”

Knix added, “Additionally, all of the fabrics in our gusset technology are OEKO-TEX certified for safety.”

FWIW, if you recall, Thinx also said its products are OEKO-TEX standard.

Knix also weighed in with its two cents on why Thinx may contain toxic chemicals: “We suspect that part of the chemical issue with Thinx is in the stain proofing technology, which is something that Knix underwear doesn’t have. We’re putting our fabric to some additional tests and we’ll have more info soon.”

This isn’t the first time Thinx has experienced controversy. Back in 2017, the firm’s former head of PR, Chelsea Leibow, filed a sexual-harassment complaint against ex-boss Miki Agrawal, the Canadian-born founder and former CEO of the brand. Though the two parties ending up settling and the complaint was withdrawn, Agrawal was ousted from her own company. (She has since gone on to found bidet-attachment company TUSHY.)

We wait with bated breath to see what happens next in this saga.

This post has been updated to include a statement from Knix CEO and founder, Joanna Griffiths.