Do Microwaves Kill Germs Like Viruses and Bacteria?

Published March 11, 2020
Woman Adjusting Temperature Of Microwave Oven

Can a microwave kill germs like flu viruses, coronaviruses, and harmful bacteria? The short answer is yes, but not evenly and maybe not in the way you think. Unfortunately, there's no standard set of guidelines for exactly how to kill the different types of germs you might be concerned about on foods, medical devices, and other objects. Here's what is known so far and how you can use your microwave to kill some germs.

The Facts About Killing Germs in the Microwave

A popular study from 2007 by a group of University of Florida professors looked specifically at using a microwave oven to kill the bacteria on a sponge. They found that microwaving a wet sponge on the highest setting for two minutes killed or deactivated 99% of all the living pathogens in the sponges. A more recent study by Cardinale, M., Kaiser, D., Lueders, T. et al. found that microwaving things like sponges might kill some of the weaker bacteria, but it could make the strong bacteria even stronger. Other experts suggest the findings of this study were misleading, indicating that the most harmful germs will be inactivated. The take-away is that microwaving will likely help, but it may not offer a 99% improvement and may vary with the pathogen you're trying to kill.

Microwaves Kill With Heat, Not Actual Microwave Radiation

Over time, researchers have learned that it is the heat, not the actual microwaves, that can disinfect an item. Normal cooking methods, like baking, frying, or microwave cooking, do kill bacteria and viruses in foods when all parts of the food are brought to a proper temperature. How high the heat needs to be varies with the type of virus or bacteria, but here are some important examples:

Microwaves Do Not Disinfect Evenly

Anyone who has reheated some leftover lasagna knows that microwaves don't heat evenly. This means they don't bring all parts of an item up to the same germ-killing temperature. Some parts may be hot enough to kill germs, leaving only parts of an item disinfected.

How to Kill Germs With Your Microwave

According to the Centers for Disease Control and Prevention (CDC) in a 2019 report, the use of microwaves to sterilize medical devices is not approved by the Food and Drug Administration (FDA). Medical devices could include common household devices like thermometers and medical masks. The CDC shares previous research that is conflicting in showing exactly if or how household microwaves can be used for medical quality sanitation.

Woman opening a microwave oven

Microwaving Objects in Water

Because some studies have shown that microwave sanitation methods using water are effective, the CDC does recommend steaming some items in the microwave as a method of sanitization. They suggest this as a method for sanitizing baby feeding supplies after they have been properly cleaned with soap and water. While the method is suggested for baby bottles, they say it also works for feeding or medicine syringes, medicine cups, and medicine spoons.

  1. Wash items well.
  2. Place disassembled items in a microwave steaming system that you've purchased. If you don't have a steaming system, place items in a glass or ceramic container with a lid.
  3. Cook the item on high for four to six minutes. According to the CDC, most viruses and bacteria are destroyed after six minutes.
  4. Items should air dry completely before they are reused or put into storage.

Microwaving Food to Kill Germs

If you need to sterilize a food or liquid, such as take-out that you may not trust is free of germs, the key is getting it to a uniform temperature that is high enough to kill viruses and bacteria. Remember, this will not help with food that is expired or has gone bad; this is a technique you might use for food that could be contaminated. Here's how to do it:

  1. Wipe down any takeout containers you feel could be contaminated or transfer food to sterile, microwave-safe containers.
  2. Cook the food or liquid in the microwave on high. The cooking time will vary, depending on the food or liquid.
  3. Use a thermometer to check the internal temperature of the item. It should read at least 170 degrees Fahrenheit. Check in several places, and stir the food if possible to make sure the temperature is uniform.

What Shouldn't You Microwave?

Microwaves were built to heat foods and beverages, so most experts recommend you only use them as directed. There are many types of materials that should truly never be microwaved because they can cause fires or small explosions.

Putting a dish in the microwave
  • Metal, any type or amount
  • Sharp objects, like toothpicks
  • Whole eggs in their shell
  • Thin or flimsy plastics that melt with high heat
  • Paper like brown bags or newspaper
  • Containers insulated with foam
  • Styrofoam
  • Plastic bags
  • Clothing and other large fabric items like bedding

Should You Sanitize Disposable Masks in the Microwave?

Disposable medical masks are made to be used once, like a tissue. Hsu Li Yang, a programme leader for infectious diseases at the NUS Saw Swee Hock School of Public Health, says because of this you should not try to steam sanitize disposable masks in the microwave. The appliance can actually damage these thin materials and make them less effective. The FDA echoes this advice, warning that surgical masks are not meant to be used more than once.

Should You Sanitize Your Toothbrush in the Microwave?

There is no real evidence showing that using a contaminated toothbrush after an illness would recontaminate you, says the CDC. If you don't share your toothbrush and rinse it off after every use, there's no real danger in using your own toothbrush after an illness. The CDC warns that microwaving your toothbrush could actually damage it.

The Power of Heat

There's no doubt that heat can help destroy some germs like bacteria and viruses. Since your microwave oven produces heat, it's reasonable to assume it could help sanitize or disinfect different items. More research is needed to help guide people on this unintended use of household microwaves. This basic information about using microwaves to kill germs should give you a good idea whether this is the method you want to use or not.

Do Microwaves Kill Germs Like Viruses and Bacteria?