Farts come in two varieties. There are family farts and there are other people’s farts. Family farts smell bad but normal. Non-family farts smell heinous. And there’s a specific scientific reason this is true. Moms, dads, and their children have similarly-scented flatulence because they have similar diets and microbiomes. As a result, dad’s war crime flatus doesn’t drive the house into disarray. Horrific smells may not even register. Farts become a joke.
All couples come to share fart scent profiles when they are sharing meals. “Food is a major driver of the microbiome because families eat together and have many shared eating patterns, therefore this increases microbes shared,” explains Dr. Terry Wahls, a physician who studies gut health. But family dinner does not, in and of itself, explain the similarities in gut bacteria that affect fart smell.
Consistent touching and cohabitation can effect microbiomes. This is why small children often have the same gut bacteria as their parents. More specifically, mothers pass their microbiome onto offspring during childbirth through exposure to feces and other means. On top of that, the chemical composition of a person’s farts goes back to DNA. Smelly farting parents have smelly farting kids.
“Your ability to produce significant quantities of methane—one of the multiple components in intestinal gas—is based on genetics,” dietician Tracy Lockwood told Men’s Health. “The offspring of two methane producers have a 95 percent of being a methane producer.”
From an evolutionary perspective, bad smells are meant to signal a threat to humans for the sake of their survival. However, when people encounter the same bad smells over and over again without becoming sick or injured, their bodies are primed to habituate to these smells over time. Since the smell of your own farts does not kill you, it makes your ability to recognize them weaker.
“In nature, survival depends on your ability to detect other smells, so you tend to ignore your own,” Loretta Breuning, founder of the Inner Mammal Institute, an organization that studies the brain, recently explained to Men’s Health. If families are scientifically predisposed to having the same kind of smelling farts, then moms, dads, and kids would likely habituate to each other’s flatulence the same way.
Science aside, most parents are inured to their children’s output during the diapering and potty training processes. So they can get past the occasional pffft. That said, they may want to advise against such indiscretions when guests come over.