8 Things You Never Clean but Should

“Food gets left in there and it can start to smell,” admits Haley F. Oliver, a professor of food science at Purdue University. “You end up rewashing your dishes with old dirt.”​

To clean out trapped food particles, unscrew the screen from the dishwasher floor and remove the filter; use dish detergent and a brush to scrub the filter and let it air-dry. Oliver suggests cleaning the dishwasher filter every week. ​

After that, clean the inside of the dishwasher. Fill a dishwasher-safe mug with white vinegar, and run it on the “normal” cycle with hot water to loosen soap scum and grease from the interior.

3. Oven

Scrubbing the burned foods crusted on the bottom of the oven and the grease coating the oven door might be the least appetizing item on a housecleaning to-do list. Although Oliver notes that temperatures get so hot inside the oven that bacteria have no hope of survival, germs are not the sole reason to get out the scouring pads.​

“Nothing ruins a delicately flavored food like burning in the bottom of the oven,” Oliver says. “You end up with cupcakes that taste like char.”​

A dirty oven could also cause a grease fire. ​

The self-cleaning feature is a good default, but nothing matches the effectiveness of some old-fashioned elbow grease. Oven cleaners often contain harsh chemicals, but lemon juice, baking soda and vinegar can get the job done without the lingering smell of chemicals tainting the next meal you cook.​

4. Ceiling fan blades

Turning on the ceiling fan might offer a cool breeze on a hot, humid afternoon, but it also scatters the dust and pollen that collect on the fan blades. Cue the sniffling and sneezing.​

“Ceiling fans cause problems by increasing circulation of airborne allergens,” says Hugh H. Windom, M.D., allergist and founder of Windom Allergy, Asthma and Sinus in Sarasota, Florida.

To ensure your allergies don’t flare each time you switch on the ceiling fan, wipe the blades down with a damp cloth.​

5. Reusable shopping bags

Admit it: The bags you toss in your trunk after every shopping trip have never seen the inside of the washing machine. These oft-used, never cleaned bags are breeding grounds for bacteria. And the number of bacteria multiply tenfold when a reusable bag with leaked meat juice gets left in the trunk of a car for two hours.​

“In a lot of these reusable bags, we found more E. coli and fecal bacteria than you do in your underwear,” says Charles P. Gerba, microbiologist and professor at the University of Arizona. “If you use the same bags to carry raw meat products and raw vegetables, you could make a salmonella salad really easily.”​

Gerba suggests sticking with cloth bags that can be washed, and tossing them in the machine (washing in hot water) after every use. It’s also a good idea to designate separate bags for meat and produce.​

6. Dryer vent

You know that a clogged lint screen is a fire hazard, so you clear it out after each load. But when was the last time you cleaned the dryer vent? Lint can also get trapped in the vent that runs from your dryer to the outside of the house — and failure to clean it is linked to $35 million in fire losses every year.​

Use a skinny brush with a long handle to remove lint from the vents; a pro can also come in to do the job. The good news: You only need to do it every three months. ​

7. Mattress

Even though the average person changes their bedding every 24 days, most likely ignore their mattresses. In fact, a 2018 study published in Royal Society Open Science compared the number of bacteria in chimpanzee beds to that in human beds. Our primate ancestors maintained cleaner sleeping environments, with just 3.5 percent of bacteria coming from their skin, saliva and feces compared to 35 percent in human beds.​

To clean your mattress, strip off the bedding and vacuum the entire mattress, paying special attention to the crevices where dirt and dust collect. Use a stain remover to spot treat stains, sprinkle baking soda over the mattress to deodorize, and vacuum again to remove the baking soda. Plan to repeat the entire process every six months.​

8. Kitchen sponge

Your kitchen sponge might be dirtier than the surfaces you’re trying to clean. In one study, researchers found 309 different species of bacteria, from salmonella to listeria, on kitchen sponges. Concentrations were as high as 45 billion bacteria per square centimeter. ​

“Bacteria grow to huge numbers because [sponges] are moist and always picking up food for bacteria to munch on,” Gerba explains. ​

Nuking a sponge in the microwave might kill bacteria, but replacing your germy kitchen sponge on a regular basis might be better. Research suggests that the strongest bacteria may survive the microwave, leaving your sponge even more stinky and germy than ever. ​

Bacteria counts are highest after three days, according to Gerba. After that, replace your old kitchen sponge with a new one.

​No one wants to spend more time cleaning, but the extra effort will leave you with a healthier home.

Editor's note: This article was originally published on March 1, 2022. It has been updated to reflect new information.