What 0.0001 Is Left Over When You Kill 99.9999 Percent of Bacteria?

According to a microbiologist, “It’s safer to make a sandwich on your toilet seat than a cutting board."

What 0.0001 Is Left Over When You Kill 99.9999 Percent of Bacteria?

Few things are more human than our collective yearning for absolutes. Which is why everyone loves antibacterial cleaning products that claim to kill 99.9 percent of bacteria.

And it’s actually even better than that. According to Charles Gerba, a microbiologist at the University of Arizona whose research focuses on the transmission of pathogens by water, food and fomites, the actual percentage of bacteria that’s eliminated by antibacterial cleaning products is closer to 99.9999 percent. “Some will kill even more, but a consumer doesn’t care about 99.9999 percent,” says Gerba, who believes that two decimal places is about as far as the average consumer will understand.

Gerba, however, isn’t as concerned with bacteria as he is with viruses. “It takes thousands of bacteria to have any effect, but it only takes one virus,” he explains. It’s because of this mix of harmful organisms that most antibacterial soaps claim they kill 99.9 percent of “germs,” a word which refers to both bacteria and viruses. (No disinfectant will work for every application and in every setting.)

Either way, you’re mostly worrying for nothing. Gerba says the chances of being affected by a surface that’s recently been cleaned with antibacterial cleaning products is about 1 in 10,000. Plus, he adds, it’s the unlikely culprits that do the most damage. “It’s safer to make a sandwich on your toilet seat than a cutting board,” he says, explaining that the average cutting board — which frequently comes into contact with raw meat and organic root vegetables — is coated in 200 times more fecal matter than a toilet seat.

If you really want to get sick, though, just touch a shopping cart. This is the single most likely place a person (especially a child) is going to contract e. coli: “If your kid is constipated, take him to the market and put him in a shopping cart,” Gerba jokes.

That said: “Unless you have a weakened immune system and you’re exposed to thousands of bacteria or pathogens, things like bacterial spores (extremely resistant bacteria), aren’t going to affect you,” Gerba explains.

So for all you Howard Hughes–type germaphobes out there, 99.9999 percent isn’t 100 percent, but ask yourself this: Is anything?