Doorknobs and toilet seats are on your radar. But your toothbrush holder?

That dingy cup is the most bacteria-ridden item in your house. And it’s not even a close contest, according to a study from NSF International, which certifies food, water, and other products for consumer and environmental safety.

The NSF team found roughly 3.3 million microorganisms per 1.5 square inches of toothbrush holder. The second filthiest thing they identified (more on that in a minute) packed just 28,000 germs in the same amount of space.

The authors of the NSF study said there are two reasons your toothbrush holder is a cesspool of germs. For one thing, you probably never clean it. And for another, it’s likely sitting near your toilet.

When you flush, bacteria in your toilet water become “aerosolized,” or airborne. It then floats onto stuff in its immediate proximity. While you probably clean or replace most of that stuff—towels, toiletries—and you rinse your toothbrush twice a day, your toothbrush holder just sits their collecting creepy crawlies.

So give that sucker a scrub. While you’re at it, clean up the other gross items on this list:

Rags and sponges are designed to suck up and hold liquid, which makes them ideal for trapping germs, the NSF study authors say. That’s why an old sponge or rag came in second on their list. It’s time you got a dish brush—the kind you can throw in your dishwasher or let soak overnight in soapy water.

Maybe you recall that the machine’s instructions told you to flush out your maker’s reservoir every once in a while. Of course you never have, which explains why a recent study found 50% of these water reservoirs are lined with mold or yeast. For most machines, you need to cycle through some white vinegar every couple months.

Car or house keys are often the filthiest things people touch on a daily basis, finds another NSF study. Your computer keyboard is also riddled with germs—up to five-times more than you’d encounter on a typical public toilet seat, finds an analysis from UK researchers. Disinfecting wipes are your friends.

They’re helpful for slicing and dicing because they’re soft, and so won’t harm your knife. But wood cutting boards end up riddled with knife marks, which act like little beds for bacteria to bloom. At least once a week, slop on white vinegar to clean and disinfect, then scrub that sucker down with dish soap. Buying plastic boards you can put in the dishwasher also helps.

They dangle and brush against all the filth you walk through, but you probably don’t think about that when you’re tying them. It’s time you started. A University of Arizona study found shoelaces are on par with toothbrush holders when it comes to bacteria populations. Consider tossing yours in the wash with your clothes every once in a while.

When it comes to germs, your bathroom has nothing on your kitchen, finds another U. of Arizona study. And when it comes to your kitchen’s bacteria hotspots, the sink takes the prize. Give it a good scrub with disinfectant wipes or sprays every night when you clean up.

Everything you’ve heard about your phone and bacteria is true. Because you take it with you everywhere you go—and always have your hands on it—your smartphone likely holds a cornucopia of microorganisms. Wipe that bad boy down with wipes at least once every few days, the Arizona researchers advise.