Smart underwear detects lactose intolerance by tracking your farts

People have a poor grasp of how often they fart, but smart underwear can provide a more accurate measure of flatulence, helping to spot gut-related conditions that might go undiagnosed like lactose intolerance.

Brantley Hall at the University of Maryland and his colleagues have designed a small hydrogen-detecting device that you can attach to your underwear to measure the frequency of farts, or flatus. “It’s like a medium-sized coin, like a nickel or a two-pence piece, and a couple of coins thick. And it clips on adjacent to the perineum,” says Hall.

He and his colleagues got 37 people to use the device to record what happened after consuming lactose, the sugar in dairy products. Producing excess intestinal gas is a hallmark of lactose intolerance, because if people don’t have the enzyme lactase to break down lactose, microbes ferment it instead. This produces hydrogen, leading to bloating and releases of gas. The trouble is, about one-third of people with lactose intolerance don’t report symptoms – sometimes because they don’t know they are farting.

The researchers  put the participants on a low-fibre diet for two days to minimise microbiome activity and establish a baseline of farting. Then, on the morning of the third day, each person received either 20 grams of lactose or of sucrose. On the fourth morning, they consumed the other sugar. The participants and research teams didn’t know who was getting what.

Of the 37 participants, 24 were sensitive to lactose and farted over 1.5 times more than their baseline during the day after consuming it, according to the smart underwear. The day with higher gas production corresponded to the lactose consumption in 22 of these people.

But an accompanying survey revealed that the same people only correctly guessed which day they were gassier 50 per cent of the time. “It’s literally like a coin flip,” says Hall. “People aren’t reliable narrators about their flatulence patterns.”

Hall will present the results at the Digestive Disease Week 2026 conference in Chicago on 4 May. He views the device as a way to objectively determine how much gas people are producing to help diagnose conditions like irritable bowel syndrome. It could also help study how well drug treatments to reduce intestinal gas production are working, he says.

“Measuring flatulence right where the gas leaves the body by using non-invasive smart-underwear is interesting, especially given the good acceptability of the technique,” says Tom van Gils at University of Gothenburg in Sweden.

He has done work showing that the subjective sensation of flatulence is relevant as a symptom, but he says an objective measure might teach us more about the body changes involved in some gastrointestinal disorders.

Recent work from Hall and his colleagues showed that in healthy adults, daily fart count ranges between four and 59, with the average being 32.

“That figure is likely to go down over time because our studies are probably biased towards people who are farting a lot,” says Hall. “We’re trying to establish the baseline of healthy human flatulence patterns, including how many times a day people fart and what foods are the major causes.”