A company selling underwear infused with “beneficial bacteria” promises skin benefits and even frames it as skincare built into fabric. But the FAQs spell out specific washing limits, raising a basic question: do the probiotics survive real laundry?
The idea is so neat it almost sounds like a morning hack: skip the creams, skip the serums, just get dressed and let bacteria do the work.
New Scientist’s editor, Catherine de Lange, alerted the team to the latest product pitch after being sent a press release for a company called Underdays. She forwarded it to Feedback without comment—an approach the newsroom treated as a kind of silent alarm.
Underdays’ underwear is infused with beneficial bacteria designed to nourish the skin microbiome. In the press release’s own wording, “The most intimate layer just got an IQ”. The claim comes with a broader promise that “prebiotics and probiotics” are “infused into the fabric. transferring to your skin all day”. supporting the microbiome. strengthening the skin barrier. and promoting a healthier appearance.
The pitch is also sold as time-saving. “No creams. No serums. No extra steps. Just get dressed and have your skincare, woven in.”
But once the press release leans on the everyday routine—wear all day, keep your skincare simple—one practical snag moves into the foreground: washing.
Over the years, the newsroom notes, underwear needs to be washed regularly. The question is what happens to the bacteria once that regular laundry starts. Elevated temperatures and common detergent chemistry could, in principle, knock down any living microbes embedded in fabric.
To dig in. the team visited the Underdays website in private mode and scrolled past photos of different underwear to an FAQs page. The guidance there undercuts another part of the time-saving promise: the underwear doesn’t replace an existing skincare routine. Instead, it should be used “alongside your existing products”. That means the “just get dressed” framing may not be as literal as it first sounds.
Then comes the part that directly answers the bacterial survival worry—at least on paper. The FAQs recommend washing all the underwear on a cool wash, with a maximum of 40 degrees, placed in a garment bag. Users are told to air-dry flat in the shade, and “Do not iron or tumble dry.”
The same FAQ also provides a slightly different instruction: “wash at 30°C on a gentle cycle.” If you follow that. the company claims the probiotics in the underwear will last for “up to 40 washes”. The phrase “up to 40 washes” doesn’t lock in a single number—Feedback points out that it encompasses a wide range of possibilities.
Underdays did not respond to a request for comment about how this works scientifically.
For now, the pitch stands on a familiar tension: a product marketed as bacteria-forward skincare convenience, with durability dependent on careful washing rules—and with the real-world payoff still hanging on whether the microbes survive the trips from body to laundry and back.
probiotics underwear skin microbiome prebiotics laundry washing guidance garment bag 40 degrees 30°C gentle cycle
So the bacteria just… survives being washed? That seems sus lol
I read “beneficial bacteria” and immediately thought probiotic yogurt not underwear. If it says specific washing limits, then it’s basically not for normal laundry right?
My cousin has sensitive skin and everyone keeps pushing microbiome stuff, but I’m like… detergent is still detergent. Also the article says it doesn’t replace skincare and I’m pretty sure that kills the whole “no extra steps” thing.
Idk why people trust this. Like if the bacteria is “infused” then how is washing not gonna remove it. Do you air dry it on low heat like it’s a plant? Then they say it helps the skin barrier and healthier appearance… but I’m sorry my underwear already has bacteria and I’m not seeing miracles. Also the IQ line had me cracking up for no reason.