Smart underwear could reveal what your farts say about your gut

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Everyone farts. Nobody counts. That is starting to change.

At the University of Maryland, a team led by microbiologist Brantley Hall has spent years turning an unglamorous bodily function into a legitimate field of study, using a coin sized sensor called Smart Underwear that clips discreetly into the back of ordinary briefs and tracks flatulence around the clock.

It is the first wearable device built to measure human gas production in real time, and the data it has produced so far is upending decades of assumptions about what counts as normal.

For years, doctors have leaned on outdated estimates suggesting the average person passes wind somewhere between five and 15 times a day.

Those numbers trace back to small, invasive studies from the 1980s that relied on rectal tubes or on people's own memory of their bathroom habits, hardly a reliable method for tracking something that often happens while asleep.

“There are a couple of studies, but they were pretty invasive. They involved rectal tubes,” said Brantley Hall, an associate professor in the Department of Cell Biology and Molecular Genetics at the University of Maryland, who led the project. “We really haven't advanced our understanding since then.”

Hall's device is designed to fix that gap in the science. The sensor uses electrochemical technology to detect hydrogen, one of the gases produced when gut bacteria ferment the food we eat.

Because hydrogen comes exclusively from microbial activity in the gut, tracking it gives researchers what Hall describes as a continuous readout of digestive fermentation, similar to how a glucose monitor tracks blood sugar.

In a study published in the journal Biosensors and Bioelectronics: X, 38 volunteers wore the sensor for more than 11 hours a day over at least three days.

The findings blew past old assumptions. Healthy adults were found to fart an average of 32 times a day, more than double the commonly cited figure, with individual totals ranging from as few as four to as many as 59 events in a single day.

Unpublished data from later studies has pushed those extremes even further.

“We had one person farting 175 times a day,” Hall said. “Then another person, on the same diet, only farted four times.”

That gulf between individuals is exactly what the team hopes to explain.

Hall's lab is now launching a nationwide project called the Human Flatus Atlas, recruiting adult volunteers across the United States to wear the device and build the first proper baseline for flatulence, matched against diet and gut microbiome data. Devices are mailed directly to participants, meaning anyone can take part remotely.

Researchers are particularly interested in two groups sitting at opposite ends of the spectrum.

The first, dubbed Zen Digesters, eat high fibre diets yet produce very little gas, a pattern that may point to a gut microbiome well adapted to fibre.

The second, Hydrogen Hyperproducers, are simply people who fart a lot despite similar diets, and studying them could reveal what is actually driving excess gas production in the first place.

Getting the sensor comfortable enough to wear all day took the team five years of trial and error, according to Hall, who stumbled on the idea almost by accident while studying microbial metabolism in a lab.

“Someone farted on it, and we had this amazing signal,” he said of the sensor's unlikely origin story.

Beyond the novelty, Hall insists there is real medical value at stake.

Flatulence frequency and intensity can flag conditions such as irritable bowel syndrome, lactose intolerance or coeliac disease, and shifts in a person's normal pattern can signal changes in diet, stress or gut health more broadly.

The technology is not yet approved for clinical diagnosis and remains strictly for research use, but Hall believes that could change.

“We don't have medical approval for this right now, so it's for research use only,” he said. “But in the future, we'd love for clinicians and gastroenterologists to be able to look at this data to inform their decisions. To know what's abnormal, you have to understand what normal is.”

The current device only detects hydrogen, but the team is working on a future version that can also pick up methane, a gas linked to constipation.

Longer term, Hall hopes flatulence tracking could become as routine as checking cholesterol or blood pressure, giving people and their doctors a genuine fart score to work with.