‘Smart underwear’ measures how often humans fart

Everybody farts. The question is how often? And how much gas is too much gas to pass?

Those are questions that arose from frustration with a piece of lab equipment.

Microbiologist Brantley Hall of the University of Maryland in College Park and colleagues study the metabolism of gut microbes. They tried unsuccessfully to measure hydrogen production from gut microbes with a sensor in an oxygen-free chamber. Frustrated, “we took the sensor out of the chamber, and we were like, ‘Screw it. We’re going to try to measure a fart.’” So Hall stuck the device down his own pants and let rip. “And the signal was enormous.”

Inspired by that incident, the team devised “smart underwear” that can track toots, specifically the hydrogen part of farts. Hall and colleagues described their device — a small hydrogen sensor about as big around as a quarter that snaps to people’s regular underwear — in the December 2025 Biosensors and Bioelectronics: X.

In a test of the device, healthy college-age volunteers who wore sensors farted an average of 32 times a day. But that figure varied from a minimum of four flatus daily to a maximum of 59. Eating high fiber gumdrops caused 36 of 38 participants to break wind more often, the researchers found.

Hall now wants to expand the study to a much larger and more diverse group to find out how often people normally fart — and whether that changes with age, diet or other circumstances. No one really knows because until now, no one has measured flatulence in people’s daily lives.

“We know what the normal heart rate is, we know what the normal level of cholesterol is, but if you go to the doctor, they don’t know the normal number of farts,” Hall says. “If you tell them, ‘I’m farting 50 times a day,’ they don’t have really a baseline to compare that to.”

The team was “shocked by the lack of measurements of intestinal gas,” Hall says. For instance, no one knows how much people fart at night because most studies have used rectal tubes in medical settings or relied on people to record their own farts, which they can’t do while asleep. “Basically, because of the limitations of measuring farts [there is a] complete gap in our understanding,” he says. “We just genuinely don’t know. Isn’t that funny? [In] 2026 we don’t know if people are farting at night or not.”

Hall’s team launched the Human Flatus Atlas in February to build on the pilot study and pinpoint the normal range. For the Atlas project, the researchers are asking volunteers to wear the sensors in their underwear around the clock (minus 15 minutes charge time while they shower) for at least three days and up to 30 days. Volunteers also agree to photograph their food with an app on their phones.

Most people don’t even feel the device once they’ve located the right spot to attach it, Hall says. In the pilot study, people were more likely to lose or wash the device than to think it was uncomfortable and drop out of the study. And people can wear the sensor for almost all activities.

“We’ve had people play rugby, run a 5K, do hours of volleyball practice, no problem,” Hall says. But “there’s one activity that you can’t do, which is biking. Biking is out. No biking.” Bike seats hit right where the sensors attach.

The earlier study suggested that people fall into three main categories. For one group, the playground rhyme, “beans, beans, the musical fruit, the more you eat, the more you toot,” does not hold. These “zen digesters” rarely fart even when they eat lots of fiber.

On the other end of the scale are the “hydrogen hyperproducers” who fart a lot. In between are what Hall’s group is calling “normal people” though the researchers don’t yet know the true normal range. The most and least prolific tooters of the Atlas project will get 3-D-printed plaques marking status.

Like the cheese-cutting that started it all, interest in the Atlas has been huge. The initial batch of 800 sensors flew out the door in just a few days, and more than 3,500 people expressed interest. Enrollment is currently paused while the researchers make more devices but may soon open again to accept people already on the waiting list and perhaps others who join in the future.

Hall and colleagues also launched a startup company called Ventoscity to help companies that make fiber supplements sniff out flatulence caused by their products.

Excitement for the Atlas project surprised Hall. With stigma and taboos against discussing bodily functions, “you would think that this is a kind of a topic people don’t want to talk about, but almost people want to talk too much to me about it,” he says. “People are very excited about measuring farts.”