I have good news and bad news. The good news is scientific tests have found that activated carbon filters reduce odors. The bad news is they only remove the smells from the air—not from the source.

Carbon Filter Removes Odors; HEPA Filter Doesn’t

Two common types of filters you’ll find in air purifiers are HEPA filters and activated carbon filters. HEPA filters are usually made out of thin plastic fibers, and they catch particles.

Carbon filters have little pellets of charcoal. If you look closely at carbon filters, you see they have a lot of holes in them.

That’s because carbon filters work differently from HEPA filters. Carbon filters capture gases (not particles!) through a process called “adsorption.”

Many Smells Are Gases, Not Particles

The distinction between particles and gases is important because many smells come from gases, not particles. For example, if you smell a fart, you’re smelling a gas.

What that means for filtration is that activated carbon filters are generally more useful for smells than HEPA filters because carbon filters capture gases.

That doesn’t mean HEPA filters are completely useless for reducing smells. Capturing particles will reduce some amount of odors. But activated carbon will do more of the work in reducing smells. And in the case of farts, activated carbon filters are the only solution because there (usually) aren’t any particles making their way out of people’s underwear and pants!

Do Carbon Filters Actually Reduce Smells?

Believe it or not, researchers actually put farts and carbon filters to the test! They published the results in the American Journal of Gastroenterology, so we’re talking about real peer-reviewed science here!

Here’s what they did. They outfitted people with different products that contain activated carbon to remove fart smells.

Some of the products were underwear with a carbon filter sewn into it.

Some were a carbon pad you can tape onto your underwear.

Some were cushions you could sit on, with carbon inside them.

The researchers measured gases that contained sulfur, which is what makes farts smell so bad. In an ideal experiment, the researchers would wait until people fart naturally and then measure the sulfur gases, but that could take a while. So they taped a tube onto people’s rear ends to pump gas out while they were using the products. They also asked people not to actually fart during the experiment!

How’d they do? The pads and the pants removed over 50% of the smelly gases. Not bad!

The cushions did worse—about 20%. But that’s still better than nothing.

If you want to remove odors in your home, consider buying an air purifier with a carbon filter.