Knix Period Underwear “PFAS” Forever Chemicals Laboratory Results

Knix Period Underwear is very popular, but does it contain any polyfluoroalkyl substances, also known as PFAS in the crotch? Mamavation tested 17 different period underwear products (and more later) and found 65% of period underwear tested contained fluorine, which is indicative of PFAS. So how did Knix period panties fare after it was sent to an EPA-certified lab? You’ve trusted Mamavation to bring you topics like  best non-toxic cookware without PFAS, best air purifiers for the home to pull PFAS out of the air, & best organic mattresses without PFAS, now join us for the laboratory results looking to see if there is potential PFAS inside the crotch of Knix Period Underwear.

Disclosure: This post was medically reviewed by Sondra Strand, RN, BSN, PHN. This post also contains affiliate links.

Potential Health Effects of PFAS Chemicals from Research

PFAS (aka PFCs or perfluorinated chemicals, including PFOA and PFOS) are added to many products we purchase to make them “stain-resistant,” “grease-proof,” and “water-resistant.” In food packaging, these harmful chemicals are used in popcorn bags, pizza boxes, fast food canisters & wrappers, and the flat dish on the bottom of cakes. They are also in carpeting, furniture, & clothing as “stain-proof” agents.  You can also find them on non-stick pans, some tooth flosses, and cosmetics.

Here is the list of health problems (PFAS) perfluorinated chemicals are linked with.

• reduction in immunity
• metabolic diseases like obesity & diabetes
• reduced vaccination response
• cardiovascular disease
• affect the growth, learning, and behavior of infants and older children
• increased risk of allergies & asthma in young children
• lower a woman’s chance of getting pregnant
• increase the chances of miscarriage
• increase cholesterol levels
• low sperm count
• smaller penis size
• increase the risk of cancer like testicular & kidney cancers

Our government believes PFAS is so problematic, it forced one dairy farmer to euthanize over 4,000 cows that were contaminated with this chemical. In other words, this is a big deal to us and the environment and it’s not a good idea to have it around your vagina.

“These results add to the growing body of evidence reaffirming that we need to know more, not less, about the ingredients in period products. Millions use menstrual products monthly. It is unacceptable that there are so many unknowns about the ingredients, safety, and health impacts of products that come into contact with one of the most sensitive and absorbent parts of the body,” said Alexandra Scranton, Director of Science and Research at Women’s Voices for the Earth (WVE), a national environmental health organization, that has been advocating for ingredient transparency and safety of period care products for the last decade. “Furthermore this new testing also shows that PFAS-free period underwear is possible. Which means, not only are these chemicals adding potentially harmful exposure to our bodies and the environment, but they are also unnecessary to the performance and efficacy of these products.”

If you feel like you’ve been exposed to PFAS, the Agency for Toxic Substances and Disease Registry, a division of Community Health Investigations has created this fact sheet to use when talking to your doctor.

14,000+ PFAS “Forever Chemicals” Are Impossible to Test For Directly

Because there are over 14,000 of these PFAS “forever chemicals” and testing is only available for about a couple dozen, it’s impossible to test for them all directly. This was a real big problem for the composting industry when ascertaining whether food packaging was safe to be certified as “compostable” for the gardens of consumers. So they devised a plan to test instead for fluorine, which is the chemical all PFAS chemicals have in common. Testing for fluorine and finding it at certain levels can indicate how much PFAS is inside and whether or not it was “intentionally added.”

Mamavation did this type of testing the other day when we tested the top period underwear products for PFAS and found 65% of them contained fluorine, meaning the period underwear industry has a big PFAS problem as well.

Because testing for fluorine is the only standard that is in use, we’ve adapted this to fabrics and are using it for our investigation on fibers & fabrics.

Lab Results of From Testing Knix Period Underwear

An EPA-certified laboratory conducted tests of Total Fluorine by Oxygen Flask Combustion and Ion-Selective Electrode on Knix Period Underwear. The Level of Detection was 10 ppm.

The Knix period underwear were purchased between May of 2020 and December of 2020 and the packaging was not opened. The contents inside were only handled by the laboratory, so these were not MY used period underwear, but a brand new pair.

• Knix High Rise–373 parts per million (ppm) fluorine detected
• Knix Boyshorts–43 parts per million (ppm) fluorine detected
• Knix High Waisted–17 parts per million (ppm) fluorine detected

So what does this mean? The Knix High Rise period underwear had some of the highest levels tested in our study. We found that incredibly ironic considering they market themselves “100% free from PFAS” and led a charge against Thinx in 2020. The claim that they are free from PFAS is simply not true and based on how they have gone after their competition Thinx (while ironically not being any better) is for Knix, a potential legal problem.

Because Knix Period Underwear was found with contamination at some of the highest levels compared to other brands, we cannot recommend this brand.

To view the entire period underwear investigation and the side-by-side results of 17 different products, click here.

Period Underwear Brands We Tested With No Detectable Fluorine

Mamavation used an EPA-certified lab to do this testing. No fluorine was detected in any of these products sent to the lab in 2020 and 2021. The Level of Qualification (LOQ) for testing was 10 parts per million, therefore if products had fluorine at lower levels, the test would not find it. We cannot guarantee these brands will continue to test the same. This was only a snapshot in time to help guide you in purchases.

• Lilova (no fluorine detected)(*newest brand added) Use discount code “MAMAVATION15” for 15% off your order. 
• Aisle (formerly known as Lunapads) (no fluorine detected) Use discount code “MAMAVATION” for $10 off any order over $35
• Bali Women’s Beautifully Confident Light Leak & Period Underwear (no fluorine detected –testing in 2023)
• Bambody (no fluorine detected testing in 2021)(additional testing in 2023 was non-detect for organic fluorine)
• Innersy Big Girls Period Underwear — non-detect organic fluorine testing update 6-23-23
• Intimate Portal (no fluorine detected)
• June Period Underwear (no organic fluorine detected) (Updated: 4/27/23)
• Period (no fluorine detected) Use discount code “MAMA” for a special sale of “Buy 3 panties and get 1 free”
• Modibodi (no fluorine detected) Use discount code “MAMA10” for 10% off orders over $100 for new customers. Not to be used in conjunction with any other offer, on sale, gift cards or bundle packs. Limit one per customer.
• Revol (no fluorine detected) Use discount code “MAMAVATION” for 15% off your first purchase.
• Saalt Period Underwear— non-detect organic fluorine result 2023. (Prior testing in 2021 had a detection of 10 ppm fluorine. Kudos to Saalt for fixing this issue!) Use discount code “MAMAVATION” for 15 % off your first purchase. One use per customer, excluding bundles.

Other Period Underwear Tested by Mamavation’s Lab

These brands were either tested for fluorine or organic fluorine at the detection limit of 10 parts per million (ppm). Some were made from organic cotton, while others were made from spandex, polyester, nylon, or conventional cotton. It seems as if indications of PFAS are prevalent in the industry as part of its product design especially when you see marketing of “moisture wick fabric.” Mamavation has also tested tampons & sanitary pads for indications of PFAS. A class action lawsuit has been filed against Thinx and Knix for misrepresenting the toxicity of their product.

• Thinx Period Underwear – Bayshort–619 ppm fluorine
• Thinx Period Underwear – High Waist–940 ppm fluorine
• Thinx Period Underwear – BTWN–132 ppm fluorine
• Knix Period Underwear – High Rise–373 ppm fluorine
• Proof Hipster–234 ppm fluorine
• Cora Period Underwear–14ppm & 13ppm organic fluorine* (new brand added)
• Knix Boyshorts–43 ppm fluorine
• Knix High Waisted Period Underwear–17 ppm fluorine (new results added)
• Joyja Period Underwear –18 ppm fluorine
• Maxim Hygiene Period Underwear–26 ppm organic fluorine (new brand added)
• Panty’s Period Underwear— 37 ppm organic fluorine (new brand added)
• RAEL Period Underwear— 15 ppm organic fluorine & 10 ppm organic fluorine (Update: 4/27/23)
• Red Ruby Box Period Underwear –27 ppm & 22 ppm fluorine
• Saalt Wear Period Underwear –10 ppm fluorine
• Sustain Natural Period Underwear –71 ppm & 17 ppm fluorine
• Thinx Speak High Waist Period Underwear –10 ppm fluorine
• Victoria’s Secret Period Underwear –20 ppm & 12 ppm fluorine