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Psst. Hey! Did you know that many microwaves have filters on them? And that they're supposed to be cleaned and/or replaced on the regular?!

Yup, file this under another one of those home maintenance facts that most of us have no idea about...but that actually should be taken care of pretty frequently.

Most over-the-range microwaves contain a grease filter, a charcoal filter or both. "Grease and charcoal filters are great for cleaning and then recirculating air inside the microwave, as opposed to venting the air outside of the appliance. This helps avoid a buildup of grease and odors," explains Leanne Stapf, COO of The Cleaning Authority.

And in order to keep your microwave — and the air in your kitchen! — clean, regularly cleaning and replacing those filters is a must. Here's everything you never thought you needed to know about these two microwave parts that you had no idea existed. Plus, what happens if you just keep on ignoring them.

Underneath your microwave is a rectangular silver plate with lots of tiny grates. Go ahead and take a look! ​That's​ your microwave's grease filter, and it's pretty important.

"The purpose of grease filters is to help catch grease that splatters up from your stovetop before it reaches the exhaust fan," says Lindsay Jones, new product brand manager for Maytag.

Catching all that gunk can help keep nasty, smelly air laden with food particles from circulating around your kitchen when you run the microwave. So, y'know, your bowl of popcorn smells fresh and buttery instead of like old food.

Once a grease filter gets clogged up, it stops being effective. "If a grease filter isn't cleaned frequently enough, grease and leftover food odors will continue to accumulate [around the filter], creating a dirty atmosphere," Stapf says.

In other words, you'll get oil bits and food gunk floating around in the air. No, you won't be able to ​see​ them. But you might smell an off odor when you run the microwave, and of course, you'll be breathing the stuff in. Gross.

Grease filters do best with a seasonal scrub. "As a general rule of thumb, you should clean your grease filter at least every three months," Jones says.

It's worth checking the manufacturer instructions for your microwave, though. Whirlpool, for instance, suggests cleaning the grease filter once a month, while GE Appliances says you can get by with a cleaning every six months.

De-gunking your grease filter might be pretty gross the first time around, but once you're keeping up with the cleaning regularly, it probably won't be a herculean task. Here's how to do it:

Your microwave's charcoal filter looks a lot like the grease filter, but it's tucked inside your microwave, typically behind the vented panel that sits on top of the microwave door. Even if you've never taken a single look at it, it plays a worthy role in your kitchen.

"Charcoal filters absorb unwanted odors in the air while cooking, made possible by the pores on the charcoal's surface," Jones says. "Especially for microwaves that recirculate into the home, the charcoal filter is key to helping get rid of leftover smells after cooking odorous foods."

A charcoal filter that's plugged up with gunk can't keep absorbing odors, which means you might start to notice a funky or unpleasant smell in your kitchen while the microwave is running, say Jones and Stapf.

That's not all: A too-dirty charcoal filter forces your microwave to work harder when it's heating food, Shapf notes, because extra grease and gunk can end up in your microwave's exhaust. And the added strain can shorten the life of your unit.

Charcoal filters typically need to be replaced (as in, buy a new one — don't clean the old one) every six months, Jones says.

If you want to try to get by with doing it less often, check the filter to see how much build-up is on it. If the surface of your filter appears totally shiny and filled with grease, that's a sign that it's hit max capacity and needs to be replaced, according to GE Appliances.

Replacing your microwave's charcoal filter is another relatively easy task. You'll just need to make sure you have a few tools handy and the right replacement filter.

Gunked-up microwave filters aren't typically a life-or-death situation. But going too long without cleaning or replacing them can cause grease and odors to build up in the appliance, which can smell funky and possibly shorten the lifespan of your microwave, says Stapf.

Plus? The longer you go without cleaning your filters, the more tedious the job will be when you finally do it. "After years of buildup, filters can get more difficult to clean," Jones says.