3 Things Everyone Gets Wrong About Disinfecting with Bleach

Household bleach can be an effective way to stave off germs, including the novel coronavirus (it’s one of the three disinfectants the CDC is recommending right now, along with alcohol and any EPA-registered product). But you need to make sure you follow expert instructions to properly disinfect, such as diluting bleach in the proper ratios, and making sure you’re mixing the solution immediately before you need it.

Here are a few common mistakes you might be making.

It may seem counterintuitive to add water to bleach, but dilution is actually the most important step in effectively disinfecting. According to the Scripps Research Institute, bleach is more effective at killing germs when diluted than when used straight out of the bottle. (But never, ever mix bleach with anything but water.)

If you’re disinfecting a hard, non-porous surface like your doorknob or faucet handle to guard against the novel coronavirus, the CDC recommends using this diluted bleach solution: mix 5 tablespoons (⅓ cup) of bleach per gallon of water, or if you need a smaller amount of solution to treat a smaller surface, 4 teaspoons of bleach per quart of water. The CDC’s other recommendations for safe bleach application include ensuring a contact time of at least one minute, and allowing proper ventilation during and after use.

If you dilute your bleach into an ordinary spray bottle, the bleach can react with the metal parts of the trigger spray nozzle and cause rusting that can further reduce the effectiveness of your cleaner, according to Jessica Ek, director of digital communications at the American Cleaning Institute. Even Clorox’s in-house experts say they do not recommend making or using a bleach spray solution at home.

If you’re using a home-diluted bleach solution, the best method is to apply it with a rag that’s saturated enough with the diluted bleach to allow the surface you’re treating to remain visibly wet for at least one minute of contact time.

Commercial sprays that contain bleach are packaged with potential reactions in mind, and any metal parts in their assembly are specially-treated to avoid causing a rust reaction with the bleach, unlike the off-the-shelf spray bottles you might buy for mixing homemade cleaners.

There’s a timeline to bleach’s superpowers. Since bleach is more unstable in its diluted form, which causes it to degrade in effectiveness, the best practice is to mix your bleach solution fresh for every application. “Diluted bleach can degrade due to temperature, light or contamination, causing the active ingredient to break down into salt and water,” says Ek. “If you want to use bleach for disinfecting, you should use a freshly mixed solution.”

Not sure you’ll have time to prepare a solution at the time you’ll need to disinfect a surface? An alternative, Ek says, is to skip the dilution step altogether by using an off-the-shelf bleach-containing disinfecting product. Those commercial disinfectants stay shelf stable for longer, and the label will tell you exactly how long it’s safe to store and use.

Even concentrated bleach should be tossed after some time. “Typically after opening a one-gallon container of bleach, it should be used up within three months or disposed due to its inability to render potential biohazards neutral,” according to the American Cleaning Institute. Whenever you open a bottle of bleach, the first thing you should do is mark the date on the bottle with a permanent marker.