• Keyboard/mouse: 79,000
The dirt: Janitors rarely touch your personal space, so if you don’t clean it, no one will.
To clean: Use sanitizing wipes to wipe every surface of the keyboard (use cotton swabs to get between the keys) and mouse and all around your workstation. Do it at least weekly, or more if you are sick or other people use the computer.
• Cutting board: 61,597
The dirt: Raw meat and chicken can make cutting boards a dangerous source of cross-contamination if they’re not cleaned properly.
To clean: For wooden boards, scrub with hot soapy water to remove soil, then do it again to kill bacteria, Duberg suggests. Plastic boards can go in the dishwasher or be soaked in a 10 percent bleach (which must then be rinsed off with soapy water) or 10 percent vinegar solution.
• Bathroom faucet handle: 50,068
The dirt: Bathrooms overall had less bacteria than kitchens, where constant contact with food adds to cross-contamination, according to one of Gerba’s studies.
To clean: Wipe with sanitizing wipes at least weekly or as needed.
• Remote control: 17,000
The dirt: Given that they pass between many hands, are used while snacking and rarely get cleaned, remote controls are often germ baths.
To clean: Wipe with sanitizing wipes a couple of times per week.
• Cellphone: 11,020
The dirt: Pressed against your face and mouth all day, cellphones can give germs easy access to enter your body. It’s particularly hairy if you share your phone.
To clean: Wipe with a sanitizing wipe daily.
• Doorknob: 8,643
The dirt: Though they get a bad rap, things like doorknobs and light switches usually aren’t so dirty, because people aren’t touching them very often.
To clean: Wipe with a sanitizing wipe at least weekly, more often if you are ill.
• Self-checkout touch screen: 4,500
The dirt: Touched by thousands of strangers and rarely cleaned.
To clean: Rub your hands with hand sanitizer after using, allowing them to stay wet for 30 seconds to kill bacteria.
• Kitchen countertop: 1,736
The dirt: When you bring foods and meats into your kitchen from the grocery store, open and clean them in an area away from where you prepare food, and put them into clean containers before storing them.
To clean: Create your own cleaning solution consisting of 10 percent white distilled vinegar and 90 percent water and put it in a spray bottle. Spray the counter to saturate completely, let it sit for 30 seconds to kill the germs, then wipe off. Unlike bleach solutions which only keep for 24 hours before losing effectiveness, vinegar solutions keep indefinitely and needn’t be washed off, Duberg said.
• Toilet seat: 1,201
The dirt: Because people are careful to disinfect the toilet seat regularly, it tends to be among the cleanest surfaces in the house.
To clean: Wipe with sanitizing wipes as needed, letting it stay wet for at least 30 seconds. One gross thing to keep in mind is that flushing the toilet releases bacteria-laden aerosols that settle on bathroom surfaces. So consider keeping your toothbrush in a drawer.