A nutritionist has outlined why some farts smell worse than others, and when the odour could be a sign you should speak to your GP.
As unpleasant as it might be, passing wind is a normal bodily function. Most people fart somewhere between 15 and 25 times a day.
In many cases, flatulence doesn’t have much of a smell at all. The sound is often what draws attention, but from time to time the odour can be noticeably stronger — and there’s a clear reason why.
A common belief is that vegetables are the main culprit behind particularly pungent farts. However, nutritionist Adrienne Benjamin says it’s not quite that simple.
Benjamin explained: “Most intestinal gas is actually odourless. The main gases we pass; nitrogen, hydrogen, carbon dioxide, methane and oxygen, don’t have a smell. The odour comes from trace gases produced when gut bacteria ferment undigested food, particularly sulphur-containing compounds such as hydrogen sulphide.
“Whilst many people blame vegetables for smelly farts (and some vegetables do contain relatively high levels of sulphur), animal products such as meat, dairy and eggs contain more sulphur and are more likely to cause ‘smelly’ fermentation.
“So it’s not the volume of gas that determines smell, it’s the type of fermentation happening in the gut and which bacteria are involved.”
Passing gas is generally nothing to worry about — even when it’s not exactly pleasant. But there are situations where a strong or unusual smell, especially alongside other symptoms, may be worth paying attention to.
If excessive wind comes with ongoing discomfort, it could point to an underlying digestive issue. Conditions such as irritable bowel syndrome (IBS) can affect how food is broken down and how much gas is produced, so it may be worth getting checked.
Benjamin continued: “Concern arises if gas is accompanied by persistent abdominal pain, unexplained weight loss, changes in bowel habits, blood in stool, severe bloating, or if symptoms are new and worsening.
“If symptoms are frequent or disruptive, it’s worth speaking to a GP to rule out conditions such as lactose intolerance, coeliac disease, IBS, or other digestive disorders.
“In many cases, gradual dietary adjustments, mindful eating, reducing ultra-processed foods, managing stress, and supporting the gut microbiome with targeted probiotics.”
She also highlighted how certain “sulphur-rich” foods are more likely to influence the smell, including eggs, garlic, onions, red meat, broccoli and cabbage.
“Hydrogen sulphide is the compound largely responsible for the classic ‘rotten egg’ smell,” the nutritionist said.
“The effect isn’t immediate. It usually takes several hours, often 6–24 hours, because the food must travel to the large intestine where bacterial fermentation occurs.”