We spend so much time worrying about what food might have picked up from the floor, but we don’t worry about touching the refrigerator. We also don’t seem as worried about food that touches the counter. But the counter is just as dirty, if not dirtier.

The same thing happens in the bathroom. I know a lot of people who are worried about the toilet seat, but it’s cleaner than all the things in the kitchen I just mentioned (0.68 colonies per square inch). What’s dirtier in the bathroom? Almost everything. The flush handle (34.65 colonies per square inch), the sink faucet (15.84 colonies per square inch) and the counter (1.32 colonies per square inch).

Things get dirty when lots of hands touch them and when we don’t think about it. We worry about the floor and the toilet seat, so we clean them more. We don’t think about the refrigerator handle or the faucet handle as much.

If we carry this logic out further, there are things we handle a lot and never really clean. One study, for instance, found that about 95 percent of mobile phones carried by health care workers were contaminated with nosocomial bacteria. Of those contaminated with staph aureus, more than half were contaminated with methicillin resistant bacteria (MRSA).

Think about how many people have handled the money in your wallet. A study of one-dollar bills found that 94 percent were colonized by bacteria, 7 percent of which were pathogenic to healthy people and 87 percent of which were pathogenic to people who were hospitalized or who had compromised immune systems. Where do you keep your money? In a wallet or purse? When did you last clean it? It’s probably filthy.

I see people pay for food every day and then eat what they’re handed with no concern that the food might have been contaminated. And the money and the hands that just held it could be much dirtier than the floor.

There are so many studies out there showing that things we touch every day are so, so dirty. Gas pump handles. A.T.M. buttons. Remote controls. Light switches. Computer keyboards.