No, smelling farts is not good for you. This idea comes from a real study that got wildly misinterpreted in headlines, but the actual science has nothing to do with inhaling flatulence. Here’s what really happened and why the distinction matters.
Where This Claim Came From
In 2014, researchers at the University of Exeter published work on a lab-made compound called AP39, which delivers tiny, controlled amounts of hydrogen sulfide directly into the energy-producing centers of cells (the mitochondria). Hydrogen sulfide is the gas that gives farts their rotten-egg smell. When media outlets picked up the story, headlines morphed “scientists designed a molecule that delivers hydrogen sulfide to cells” into “smelling farts prevents cancer.” The researchers themselves pushed back, but the myth stuck.
AP39 is nothing like a fart. It’s a precisely engineered molecule that attaches to mitochondria and slowly releases hydrogen sulfide exactly where it’s needed. In mouse studies, AP39 improved motor function after stroke, reduced damage to brain tissue, and protected heart cells from stress-related aging. But these results came from injecting a targeted compound into lab animals, not from anyone sniffing gas.
What Hydrogen Sulfide Actually Does in Your Body
Your body already makes hydrogen sulfide on its own. It’s one of several signaling molecules your cells use to regulate basic functions, and it plays a surprisingly important role in cardiovascular health. Research published by the American Heart Association describes it as a potent anti-inflammatory molecule with blood-pressure-lowering effects. It works partly by preventing white blood cells from sticking to blood vessel walls, a process that drives inflammation, and partly by relaxing blood vessels to improve circulation.
Mice that were genetically engineered to stop producing hydrogen sulfide developed significant high blood pressure and impaired blood vessel function. When researchers gave those mice compounds that restored hydrogen sulfide levels, the problems improved. The gas also acts as an antioxidant, neutralizing harmful molecules that damage cells. So hydrogen sulfide is genuinely useful to your body, but the key word is “endogenous,” meaning your body produces it internally, in precise amounts, right where it’s needed.
Why Inhaling It Doesn’t Work the Same Way
The hydrogen sulfide in flatulence is present in vanishingly small amounts. According to the Agency for Toxic Substances and Disease Registry, concentrations in farts top out around 18 parts per million on a normal diet, and the gas makes up at most 10% of intestinal gas overall. At those levels, you’re barely registering the smell.
Even if the concentration were higher, breathing in hydrogen sulfide gas doesn’t deliver it to your mitochondria. The whole point of AP39 is that it uses a chemical “address label” (a molecule called triphenylphosphonium) to find and enter mitochondria specifically. Inhaled gas doesn’t have that targeting mechanism. It enters your lungs, hits your bloodstream, and gets processed in ways that are entirely different from a controlled, slow-release compound designed for intracellular delivery.
At higher concentrations, hydrogen sulfide is genuinely dangerous. OSHA sets workplace safety limits at just 10 to 20 ppm for extended exposure. At 100 ppm, you lose your sense of smell within minutes and may experience coughing, drowsiness, and throat irritation. Between 500 and 700 ppm, you can collapse within five minutes. At 700 to 1,000 ppm, a single breath can cause immediate unconsciousness and death within minutes. This is an industrial hazard, not a health remedy.
What Fart Smell Can Tell You About Gut Health
While smelling someone else’s gas won’t improve your health, the smell of your own gas can occasionally be informative. Hydrogen sulfide in your intestines is produced by certain gut bacteria as they break down sulfur-containing foods like eggs, cruciferous vegetables, and meat. Unusually foul-smelling gas, particularly with a strong egg-like odor, can sometimes signal an overgrowth of hydrogen-sulfide-producing bacteria in the gut. Specialized breath tests now measure hydrogen sulfide levels to help diagnose these imbalances, which can be associated with diarrhea, abdominal pain, and bloating.
A noticeable change in how your gas smells, especially paired with digestive symptoms, is worth paying attention to. It’s not the smell itself doing anything beneficial. It’s a byproduct that can serve as a rough indicator of what’s happening in your digestive system.
The Bottom Line on the Science
Hydrogen sulfide is a real and important signaling molecule in your body. Targeted delivery of it to cells shows genuine promise in early-stage research for conditions like stroke and heart disease. But that research involves lab-synthesized compounds tested in animals, and as of 2025, AP39 remains in preclinical development with no human trials completed. None of this has anything to do with breathing in flatulence. The amount of hydrogen sulfide in a fart is too small to have a therapeutic effect, it can’t reach the right cellular targets through inhalation, and at meaningful concentrations, hydrogen sulfide is a lethal poison. Your body already makes exactly the amount it needs, right where it needs it.