How Cold Does the Temperature Need to Be to Kill Germs?

Published March 12, 2020
Woman putting food in refrigerator

As people look for ways to stay healthy, many wonder, "Does freezing kill germs?" The answer to this question is more complex than a simple "yes" or "no." However, most of the tools you have at home for creating cold temperatures are not cold enough to kill germs. Scientific studies and reviews from health experts can help you better understand how cold temperatures affect germs like bacteria and viruses.

Do Cold Temperatures Kill Germs?

Science and health researchers and experts agree that cold temperatures don't kill all germs.

  • Dermatologist Alok Vij shares in a Cleveland Clinic article that you need to reach a temperature of 80 degrees below freezing or even colder to actually kill bacteria and other germs.
  • In an NPR report after a 2013 E. coli outbreak, one scientist shared that they often store microbes at minus 80 degrees because it doesn't kill them, that way they can be studied later.
  • Since your household freezer is probably the coldest thing in your home, and it's only about 0-4 degrees Fahrenheit, the U.S. Department of Agriculture (USDA) says bacteria like E. coli, yeasts, and mold can all survive in your household appliances.

Cold Temperatures and Bacteria

While cold temperatures don't necessarily kill bacteria, they can slow or stop the growth of bacteria. This means the bacteria won't reproduce quickly, but it also won't be completely destroyed. For example, Listeria will stop growing completely in the refrigerator, but it doesn't die. A USDA report of safe food practices suggests that temperatures below 40 degrees Fahrenheit, which is the average temperature of your refrigerator, can stop or slow the growth of bacteria. CDC food safety guidelines suggest your refrigerator should always be between 40 and 32 degrees Fahrenheit. Any temperatures above 40 degrees allow bacteria to grow rapidly. If you chill things like foods in the refrigerator to slow the growth of bacteria, the bacteria will then be killed when you cook the food within an appropriate timeframe.

Person taking food out of freezer

Cold Temperatures and Viruses

Cold temperatures don't really kill most viruses either. You may have heard that viruses like influenza, or the flu, are caused by cold temperatures in winter. This is a myth, but a 2014 review of research by a PhD candidate at Harvard University showed that, in locations experiencing winter, influenza thrives. This specific virus seems to transmit better at colder temperatures where there are lower humidity levels. Influenza can survive for about 23 hours at 43 degrees Fahrenheit. Viruses are killed or destroyed better by heat than by cold and the need moisture to survive. This is why viruses stay contagious longer on nonporous metal and plastic surfaces than on porous items like soft toys, cloth, and wood.

Does Freezing Clothing and Fabric Kill Germs?

Now you know that freezing at home doesn't really kill any kinds of germs, but you may have heard that freezing things like jeans can be better than washing them. This is also a myth. Freezing temperatures do not sanitize laundry. Although bacteria can live off the dead skin cells, food, and dirt on your clothes, the soaps in laundry detergent are all you need to help remove bacteria from clothing. Since the water in your washing machine won't get anywhere near cold enough to kill germs, it doesn't even matter what temperature you use to wash your clothes when it comes to removing germs.

Setting temperature on washing machine

Freezing Kills Bed Bugs

While freezing fabrics won't kill germs, there is evidence that it kills bed bugs. The University of Minnesota shares that bed bugs can be killed in your household freezer. They say it's safe to put cloth items, modern books, shoes, jewelry, pictures, and toys in your freezer to kill bed bugs and their eggs. However, you have to make sure the freezer maintains a temperature of 0 degrees Fahrenheit and keep the items in the freezer for 4 days after each item's center reaches 0 degrees. You should never try to freeze items that could be damaged from condensation, electronics, or historic artifacts.

Can Cold Water or Ice Help Kill Germs?

The cold water from your faucets is usually no colder than 45 degrees Fahrenheit and can get as warm as 70 degrees depending on the source and the temperature of your home. This is not cold enough to kill most germs.

Ice and Germs

A group of researchers looking at frozen flu viruses found that the low pH of frozen water could inactivate a virus if the virus is frozen directly in water. However, once the ice begins to thaw, the bacteria can "wake" back up. The researchers also found that the freezing and thawing process does kill about 90% of a virus each time it's thawed. Another recent study of ice cubes shows they are loaded with bacteria. These bacteria aren't killed by the freezing process, but they may not be able to grow. This means that putting ice in your drink or rubbing it on your skin won't really kill any germs.

Cold Water and the Human Body

You might still be tempted to use cold water to help disinfect yourself, but cold water can be dangerous for people. It's certainly safe and just as sanitary as using warm water to use cold tap water to wash your hands. Keep in mind that most germs like cold and flu viruses are only contagious on your skin for about 20 minutes, so excessive washing isn't necessary. According to the National Center for Cold Water Safety, any water below 70 degrees Fahrenheit can be dangerous to people, especially if you are submerged in it for a long time. The cold shock of the water can cause you to lose control of your breathing.

Will Cold Temperatures in Your Home Kill Germs?

As with cold water temperatures, cold air temperatures can also be dangerous for people. Since the evidence shows colder temperatures won't really kill bacteria and germs, unless they are dangerously cold, there's no need to turn off your heat or crank up your air conditioning in an effort to sanitize your home. In fact, freezing yourself could cause you more problems and freezing your home could cause structural damage. Fresh air also won't help kill any germs, but it can help create air flow in your home to assist in removing dust or bad smells.

Germs Don't Care About Cold

Extreme cold temperatures can kill some germs, but the cold temperatures you can typically achieve at home can only slow them down. It's great that you're looking for alternatives to things like heat, alcohol, or disinfectant cleaners for getting rid of germs, but cold water or air probably isn't your best option.

How Cold Does the Temperature Need to Be to Kill Germs?