What Is The Smelliest Thing In The World?

Smell is a strange sense. We don’t really notice it all that much – we’re hardly nose-first animals like cats or dogs – but it’s nevertheless incredibly powerful. It has the power to evoke memories; to subconsciously heighten arousal or fear; to even change how we see the world around us.

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And, of course, it can make us puke.

The worst smell in the world: the contenders

The natural world is rife with things that smell, to put it bluntly, really rank. There’s the corpse flower, so named because it smells like hot death; the stinking corpse lily, which has a very similar name for a very similar reason; plus another flower that smells less of death and more like stinky socks. 

There are stinky fruits: the durian, for example, is notorious for its stench, which has caused an entire building to be evacuated on at least one occasion; the famous chef Anthony Bourdain once said that eating it will leave your breath “smell[ing] as if you’d been French-kissing your dead grandmother.”

Animals – the non-human ones, at least – often enjoy smelling bad, since it can scare away threats. That’s the logic of, say, the skunk, whose extremely potent spray is sometimes described as smelling like a mixture of rotten onions and burning rubber – more generally, a mix of something organic and something industrial. 

But while skunks are probably the most famous smelly animal, they’re positively pleasant next to some others. The lesser anteater, or southern tamandua, can release a stench spray which is up to seven times stronger than the skunk’s – and the striped polecat is reputedly even worse, with a spray so strong and disgusting that it can temporarily blind anything that gets hit by it.

They’re all good contenders for the worst smell in the world – but how can we possibly mark them against one another?

The science of stench

So, what can we glean from these potential putrescences? Are there any common themes that we can harness, perhaps, to figure out what the king of all foul stenches might be? Well, in fact, there are.

Smells are, of course, subjective – to an extent you might not quite believe: “People who live around horses like the smell of manure. Some people even like the smell of skunk,” cognitive psychologist Pam Dalton of the Monell Chemical Senses Center in Philadelphia told New Scientist back in 2001. And while for most people, the durian fruit is “almost impossible to get […] past the nose and into the mouth,” she said, in Southeast Asia, it’s perceived as pleasant.

Even when we agree on an odor being unpleasant, we can disagree on just how bad it is. For people who live without reliable modern sanitation, the smell of sewage isn’t just disgusting, it’s frightening; “For some Vietnam veterans the smell of mold, the sort you get on tent fabric, will trigger a fear flashback,” pointed out José Pardo, Director of the Cognitive Neuroimaging Unit at the Minneapolis VA and Professor in the Department of Psychiatry at the University of Minnesota. 

Nevertheless, there are some constants. We don’t tend to like smells that suggest something hazardous to health, so anything sulfuric is probably a good candidate: “If I had to predict one class of odors we had a predisposition to react negatively to, it would be the sulfur compounds,” Dalton said. “It's important to detect food spoiling or carcasses rotting. It must have significance in terms of survival.”

Human (and other animal) poop is another good choice. It’s full of bacteria and viruses – potentially parasites, too – and it’s pretty much by definition stuff we don’t want inside of us. It’s also basically universally reviled: “There aren't many cultures that embrace human waste,” Dalton pointed out.

But we can get more technical than this. It’s actually possible, to a certain extent, to objectively measure how malodorous a certain substance is going to be – even before anybody puts their nose to it. 

“What we found is the best number for describing the pleasantness of a molecule,” reported Rehan Khan, then a research scientist in the Helen Wills Neuroscience Institute at UC Berkeley, in a 2007 statement. “In other words, your nose, in telling you whether a molecule is pleasant or unpleasant, is telling you the most useful number or summary of that molecule.”

It seemed to come down to molecular weight and electron density: heavier, more compact molecules smell “bad”, and lighter, more spread-out ones smell “nice”. 

“That’s kind of freakish because we all tend to think of pleasantness as something reflecting our inner structures and desires, and history and cultures,” study coauthor Noam Sobel told New Scientist at the time. “What we are saying is no. A large part of it is written into the structure of molecules.” 

To give you an idea of how impactful this aspect of odor is, we can just look at the team’s own experiments. In one, they used their metric to order 27 chemicals from prospective least- to most-smelly; when they were assessed by humans, the rankings agreed with their predictions about 30 percent of the time.

That might not sound high, but it’s statistically significant. “When we presented the preliminary results at a conference, a fragrance company said they flat-out didn't believe us,” Khan told Live Science. When they reproduced their findings with a set of new scents, the company was “quite surprised,” he said.

The winner?

So, we have the criteria: the worst possible smell should be something with a big, heavy, compact molecule; preferably sulfur-based; potentially reminiscent of rotting food or poop. And you know what? We have just the thing.

It’s a chemical which, according to industrial chemist Derek Lowe, “makes innocent downwind pedestrians stagger, clutch their stomachs, and flee in terror. It reeks to a degree that makes people suspect evil supernatural forces.” 

People who smell it “start diving out of windows and vomiting into wastebaskets,” Lowe wrote in a 2009 article for Science. It “smells like hell's dumpster.”

The culprit? Thioacetone. Or – well, probably thioacetone: it’s hard to single out as a monomer rather than as a compound of trithioacetone, not for any particular chemistry-based reason, but because nobody can bear to be around the stuff long enough to interact with it.

If all this sounds hyperbolic, it isn’t. When the chemical was first distilled in Freiberg, Germany, in 1889, it produced a smell so strong, and so putrid, that it swept through the city “causing fainting, vomiting, and a panic evacuation” for everyone within a half-mile radius of the lab. 

If that doesn’t float your boat, there’s always US Government Standard Bathroom Malodor – a smell concocted specifically to test deodorant cleaning products. It “smells like shit,” Dalton told New Scientist, “but much, much stronger. It fills your head. It gets to you in ways that are unimaginable.”

So bad is this smell that people exposed to it started screaming and cursing after just a few seconds. “If anything transcends culture it should be something like this,” Dalton said. “This is far worse than any regular human waste.”

Of course, you could potentially make something worse than both. Part of Dalton’s research involved mixing Bathroom Malodor with another stink bomb named Who, Me? – a weapon from World War Two that Dalton described as smelling like “the worst garbage dumpster left in the street for a long time in the middle of the hottest summer ever” – to find the right recipe for the world’s worst smell ever. 

She calls the result “Stench Soup” – and according to one of the few humans to ever brave sniffing it, it’s reminiscent of “Satan on a throne of rotting onions”. And if that doesn’t take the prize, we don’t know what does.