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Ever taken a bite of something, like broccoli or kale, and thought: “Whoa that’s bitter!”? Multiply that feeling many, many times over and you’ve got denatonium, the most bitter compound we know of.

And it was discovered totally by accident. Back in 1958, researchers at a Scottish pharmaceutical company were experimenting with the anesthetic lidocaine. You may have heard of it, it’s often in those gels that you can use to help cool the pain of a sunburn.

And it’s frequently used by doctors and dentists because a quick injection of the stuff makes a small area of the body wonderfully numb. That’s because it stops up the channels in neurons that allow sodium ions to flow in and out. When these sodium channels can’t open and close properly, the neurons aren’t able to send pain signals to your brain.

And that’s great, because no one needs to feel what’s going on when their wisdom teeth are being removed. Since lidocaine is incredibly useful, the drug researchers were trying to see if they could find something similar that worked even better. But when they added a benzyl group to it, they ended up with something different, a compound that we call denatonium.

It isn’t a better numbing agent, but it does bind a different family of proteins better than lidocaine does: taste receptors. Specifically, it binds to bitter taste receptors in the Taste 2 Receptor or TAS2R family. Humans have more than forty different TAS2Rs, several of which bind to denatonium.

But that doesn’t completely explain its bitterness. Scientists think it might retain some of it’s lidocaine-like ability and block ion channels to create its super bitter taste. But they’re not sure.

What they are sure of, though, is that it’s really, really, really bitter. Denatonium, in its marketed form “Bitrex,” has held the Guinness World Record for bitterest substance for half a century. And that’s because humans can taste it in solutions at really, really low concentrations, just a few parts per million.

A sugar cube-sized amount of it can make an entire Olympic-sized swimming pool taste gross. And yet, you probably have it in your home without even knowing it. It’s odorless and colorless, so it doesn’t affect how products look or smell.

And outside of being bitter, it’s considered unreactive, so it’s basically non-toxic and isn’t destroyed by water or most other chemicals. All of which makes it the ideal stuff to put in or on things you don’t want people to swallow. You might have heard about the big fuss in 2017 when Nintendo released their new Switch game cartridges, for example, because they’d laced them with denatonium and apparently everyone noticed.

My question: Why were adults licking nintendo games in the first place? You can also find denatonium in special nail polishes designed to help stop people from biting their nails. And it’s added to everything from liquid dish detergent to industrial alcohol and antifreeze to keep people especially children, safe.

It’s even used in rat poison, turns out that rat tongues are about 30,000 times less sensitive to denatonium than we are, so it doesn’t scare them off. And its effects aren’t restricted to your tongue. You have similar taste receptors in your gut, and scientists have found that directly injecting denatonium solutions into stomachs can slow the digestion process, increase feelings of fullness, and even help lower blood sugar levels.

So they’re investigating whether denatonium, or something like it, can help treat overeating or diabetes. And taste receptors are also present on the smooth muscles of your airways. So, inhaling denatonium can lead to bronchodilation, the expansion of your airways that leads to increased airflow.

And ultimately, that means further research on denatonium could help people breathe easier. Turns out there are a lot of great ways to use super bitter compounds. Who would have thought something so revolting could do so much good?

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