The Real Reason Sloths Don't Fart

Sloths are unusual creatures. They're graceful in trees, painfully slow on the ground, and strong swimmers. And despite their charismatic facial expressions, one aspect of sloth physiology makes these slow-moving furry plant eaters not the most pleasant creature to kiss, Vox reports. (Nor, despite their appeal, are they good pets, per The Sloth Conservation Foundation).

The reason you might not want to lock lips with a sloth is the same reason sloths don't do something many other animals are known to do: They're among the few animals known to science that don't fart — not in the classical sense, anyway. Farts are a byproduct of digestion, especially plant matter, and sloths eat plenty of plants — so why don't they toot? As we all know, sloths are ... well, sloth-like, meaning slow. This applies as much to their digestion as it does to their movement.

Like how sloths only occasionally poop — they only go number two around once every three weeks or so. Their slow digestion means they have an unusual gut biome. In turn, they digest their food very slowly. Still, gasses do build up in their guts over time, and like all other creatures, that gas must go somewhere, or the poor sloth might explode. For a sloth, that gas comes out of its mouth.

At this point in the sloth-fart discussion, it might be helpful to point out that flatulence manifests in different ways, and that it naturally happens for a number of reasons. Most commonly, as mentioned, as bacteria in our intestines and stomachs help us digest our food. But as Healthline points out, there are other things that might cause a creature to fart, so while sloths don't fart because of their slow digestion — does air ever escape from their butt? You'll just have to ask a sloth.

In 2020, NHPR a New Hampshire NPR affiliate reached out to some sloth experts to ask why sloths are the way they are in this regard. And in their response, that expert said sloths, "reabsorb the gas into their gut, and then they breath it out. So they've got like fart breath, but no farting." Interestingly, birds also don't fart for the opposite reason sloths don't: Birds intestinal tracts are short, and they poop often — no farting required!

Although digestive off-gassing in sloths' guts gets absorbed into their bloodstream and escapes out of their mouth, sloths are not known to smell bad, an otherwise common misperception. Sloths not only don't fart, but most sloths also don't sweat, and though their fur is covered in algae filled with all sorts of little critters, they emit no body odor to speak of, according to the Sloth Conservation Foundation. 

Another interesting point related to sloths: The biome in their four-chambered stomachs evolved specifically to digest leaves in their ecosystem that are toxic, which is another reason they digest their food slowly, and in turn, don't fart like we do — breakdown those leaves any faster, and they might end up poisoned by their own food, per BBC Science Focus. So, all combined, the next time you share a big meal with a sloth and smell something funny, the sloth may have smelt it but it most assuredly never dealt it — and that's according to science.