What temperature kills germs? How to use heat properly to get rid of bacteria and viruses

5e6a8547235c182b98016ceb — Clothes should be washed and dried at temperatures around 140 degrees to kill germs.
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Hot temperatures can kill most germs – usually at least 140 degrees Fahrenheit.
Most bacteria thrive at 40 to 140 degrees Fahrenheit, which is why it’s important to keep food refrigerated or cook it at high temperatures.
Freezing temperatures don’t kill germs, but it makes them dormant until they are thawed.
This article was medically reviewed by Tania Elliott, MD, who specializes in infectious diseases related to allergies and immunology for internal medicine at NYU Langone Health.
This story is part of Insider’s guide on How to Kill Germs.

Germs – like viruses, bacteria, and fungus – respond differently to cold and hot temperatures. For example, the flu virus thrives in colder weather, which is why flu season is in the winter.

In general, hot temperatures are better suited to killing germs, but that doesn’t mean you should start sterilizing everything with heat. “It’s not realistic or necessary,” says Manish Trivedi, director of the Division of Infectious Diseases at AtlantiCare. “The most effective intervention to prevent the spread of germs is proper hand-washing.“

In fact, for the COVID-19 virus, the World Health Organization (WHO) warns against using temperature methods to ‘prevent’ or ‘kill’ infection: spending time in cold weather or snow, taking a hot bath, using hot hand dryers, or ultraviolet lamps has no effect on this new Coronavirus strain.

But there are other cases where high temperatures can kill germs – boiling water to kill off bacteria in food products, using a dishwasher to sterilize plates, or washing and drying clothes to decontaminate them. Here’s what you need to know.

Hot water kills germs, though it has to be very hot

According to WHO, temperatures of 140°F to 150°F are enough to kill most viruses, and boiling water makes it safe from pathogens like bacteria, viruses, and protozoa. Trivedi recommends a temperature of 160°F or greater when heating water or food products, to kill off bacteria like Legionella, a common bacteria found in water.

If you have contaminated clothes or fabrics that need to be disinfected, the UK's National Health Service (NHS) recommends washing at a high temperature (140°F), along with a product containing bleach, which will maximise the disinfectant effect.

However, that's only for high-risk clothing, like when you're sick. For regular clothing, it's the drying that counts. That's because the heat of a tumble dryer ranges from 135 to 150°F, and while a washing machine provides damp places for bacteria and fungus to spread, the dryer doesn't.

"When washing clothes and household items, most harmful microorganisms are actually killed in the dryer on high heat as opposed to the washing machine," says Trivedi.

Despite the fact that high temperatures do kill most germs, washing your hands in hot or cold water doesn't make a difference. The hot water doesn't get warm enough, and cold water is just as effective because washing your hands with soap and water is more about removing dirt and germs - rather than killing them.

The same is true of washing dishes: it's unlikely you'll get the water hot enough during a manual hand-wash to properly kill bacteria on dishes. However, an automatic dishwasher is usually hot enough to sterilize the dishes inside.

If you do hand wash your dishes, food safety guidelines suggest washing with detergent at 113°F or higher, rinsing, and sanitizing with a solution, which can be a chemical sanitizing solution or clean water of 171°F or higher.

Cooking at high temperatures can kill most germs

Most bacteria thrive in temperatures of 40°F to 140°F, or what the United States Department of Agriculture (USDA) refers to as the 'danger zone'. This is when bacteria grow, multiplying by two every 20 minutes.

To avoid this, make sure food isn't left out of the refrigerator for more than two hours (or for more than one hour, if temperatures are 90°F or above). For reference, the Food and Drug Administration (FDA) recommends that refrigerators are kept at 40°F or below, to stay out of the danger zone for bacteria.

"All bacteria have their own optimum environmental surroundings and temperatures in which they thrive the most," says Trivedi. "Some germs, known as hyperthermophilic bacteria, grow in very hot temperatures up to 250°F. However, most bacteria and viruses that are pathogenic to humans can be killed through a heat of 165ºF or higher within minutes of cooking."

According to the New York Department of Health. heating food breaks the structure of germs, which makes them unable to function. Heat kills most food-borne bacteria and viruses, like Salmonella, which is a bacteria contracted from undercooked poultry and eggs, and can cause diarrhea and vomiting.

When cooking food, it's important to ensure it's heated properly all the way through, or what's called an 'internal temperature', which you can determine with a food thermometer.

According to US Food Safety guidelines, raw meat and poultry should be heated to at least 145°F for steaks or whole cuts of beef, pork, lamb and veal, 160°F for those meats ground, and 165°F for all poultry.

Foods that are reheated, like leftovers, must be heated to at least 165ºF, and need to be stored properly within two hours of cooking, by placing it in a small container in the fridge to allow optimal cooling and prevent bacteria from growing.

Freezing temperatures don't kill germs, it just slows them down

It's a common misconception that freezing food kills bacteria. While it 'slows down' the bacteria and makes them dormant, the bacteria will begin to multiply again when it's brought back to room temperature.

E.coli, a bacteria that can cause food poisoning, is an example of a bacteria that doesn't die when frozen but is 'inactive' until brought back to room temperature. This is why cooking food to a proper temperature is important, and the FDA recommends thawing foods in the fridge, too, so that even when the food defrosts, it still doesn't enter the room temperature danger zone.

"Some sensitive germs will die when frozen," says Trivedi. "However, many pathogens will start reproducing when thawed and temperatures start to increase."

While freezing will keep food unspoiled for longer and prevent bacteria growth, it still needs to be properly handled once it's thawed. Make sure you're storing and cooking food at proper temperatures - and remember that the best way to get rid of germs in day-to-day life is by washing your hands with soap and water or using hand sanitizer when soap and water are not available.