Does heat kill coronavirus (COVID-19)? Can it disinfect face masks and packages?

Answer:

If used properly, moderate or high heat can be used to "kill" coronavirus, inactivating the virus so that it is no longer infectious. However, in many cases this may be more time-consuming than other methods such as chemical disinfection (with disinfecting wipes or sprays) and there is often no need to disinfect packaging at all if you can just remove the packaging, dispose of it (preferably by recycling), and then disinfect your hands by washing with soap and warm water or using another disinfection method.

Very low risk of COVID-19 infection from food and food packaging

The FDA has reviewed the current evidence and affirmed that "the risk is exceedingly low for transmission of SARS-CoV-2 to humans via food and food packaging." (FDA 2021). However, the FDA does note "...if you wish, you can wipe down product packaging and allow it to air dry, as an extra precaution," and provides tips for grocery shopping and safe food handling during the pandemic.

Heating kills coronavirus

Heat is very effective at sanitizing and disinfecting objects from coronavirus. If anyone tells you that coronavirus is resistant to heat, they're wrong. In fact, the SARS-CoV-2 virus that causes COVID-19 may be even more sensitive to heat than the earlier SARS-CoV virus. Experiments done in China in 2002 with SARS-CoV in culture medium (Duan, Biomed Env Sci 2003) showed that coronavirus became undetectable after 30 minutes when heated to a temperature of 167°F, but recent tests with SARS-CoV-2 in Hong Kong showed that it became undetectable after just five minutes at only 158°F (70°C). The time required to kill SARS-CoV-2 increased as the temperature was reduced, such that the time by which it was undetectable increased to 30 minutes at 132°F (56°C), two days at 98.6°F (37°C), and two weeks at 71.6°F (22°C). At 39°F (4°C) the virus remained detectable at two weeks when the experiment ended (Chin, Lancet 2020).

This suggests, for example, that if you purchase take-out food and wish to disinfect the container itself of coronavirus (as well as keep your food warm), you can simply place the container in a warm oven or warming drawer for a period of time, such as at 150°F (65°C) for 60 minutes (giving it ample time to heat up) to disinfect it. Just be sure it is not directly exposed to a heating element so as not to pose a fire hazard. Most plastic and paper containers are stable for short periods at up to 200°F (93°C). 

Theoretically, heating a face mask this way may also disinfect it. Moist heat may be better than dry heat. One way to do this, as explained by the Department of Homeland Security Science and Technology Directorate (S&T), is to use a multicooker or electric pressure cooker that has a sous vide function or equivalent capability to set the time to 30 minutes and the temperature to 149°F (65°C), placing the mask on a rack to keep the mask out of the water (binder clips can be used to elevate the rack). The bottom of the pot should be covered with ½ inch of water, and the mask should be placed in a paper bag and the bag stapled closed, before placing on the rack. Up to three masks can be nestled together in one bag. When the cycle is over, the masks should be removed and allowed to dry (about one hour should be sufficient). A complete instructional video is available on the Department of Homeland Security S & T website. A study by researchers at Stanford University found that heating N95 masks (known as respirators) at 167°F (75°C) for 30 minutes (at 85% relative humidity) did not compromise the masks, even after 20 cycles — although these researchers have subsequently cautioned that contaminated masks should not be brought into homes. (If you use an N95 respirator, you may want to watch a video from the New England Journal of Medicine that instructs health care workers on how to properly put on, take off, and test the fit of such masks and other personal protective equipment.)

Another way to use an electric cooker to decontaminate N-95 respirators is to place a towel inside the cooking pot with the respirator laying on the towel (avoiding direct contact between any part of the respirator and the pot) and heating the mask to 212°F (100°C) for 50 minutes -- which requires heating the pot to about 250°F to 300°F (120° to 150°C). The University of Illinois researchers who developed this process (and uploaded a demonstration video on YouTube) found that respirator filtration and fit were not compromised after 20 cycles of this dry heat treatment (Oh, Env Sci Tech Letters 2020).

A U.S. government laboratory heated SARS-CoV-2-contaminated N95 mask material in a dry oven at 158°F (70°C) and found that virus was undetectable at 50 minutes, but they also found two cycles of this dry heating caused the material to lose some integrity (possibly suggesting that some humidity during heating may be beneficial) (Fischer, medRxiv, 2020 — preprint).

These same government researchers found that ultraviolet light (UVC at 0.005 mW/cm²) could achieve the same antiviral effect as heat with less impact on mask integrity but required about 60 minutes and this did not factor in additional time to properly irradiate curved surfaces of the mask. They determined that vaporized hydrogen peroxide (requiring a special, enclosed incubator) was the fastest and least damaging method of decontamination, taking only 10 minutes. Spraying ethanol to saturate the mask material was a bit faster at deactivating virus but caused the greatest reduction in mask integrity (Fischer, medRxiv, 2020 — preprint).

You should not soak N95 or surgical masks in disinfectants such as alcohol or other liquids as this can compromise their electrostatic charge (reducing their filtering capability) and fit (Interview with R. Shaffer, JN Learning 2020). Researchers at Stanford University found that immersing N-95 mask material in 75% ethanol or spraying with a household chlorine bleach solution (2% sodium hypochlorite) decreased the filtration efficiency (due to loss of electrostatic charge) to unacceptable levels after just one treatment, from about 96% to 56% and 73%, respectively.

Steam treatment (material placed 6 inches above a glass containing boiling water for 10 minutes) was effective if used once, but after five treatments filtration efficiency fell below acceptable levels (85%) (Liao, ACS Nano 2020).

Note that washing cloth face masks in a washing machine should suffice to disinfect them, according to the CDC. The agency also cautions not to touch your eyes, nose, and mouth when removing cloth coverings, and to wash hands immediately after removing. 

Coronavirus lasts longer on certain surfaces, particularly surgical masks! And Omicron lasts even longer.

The Hong Kong researchers noted above also placed a small amount of the SARS-CoV-2 on a variety of surfaces at room temperature (at 65% relative humidity) to see how long the virus would last before becoming undetectable. On tissue paper and regular paper it became undetectable within just 3 hours. On cloth and on paper money, it lasted 2 days. Surprisingly and disturbingly, it lasted longest on the outer layer of a surgical mask: Virus was detectable on the mask at day 7 (although at only 0.1% of its original level), which was also how long it lasted on plastic and stainless steel. Interestingly, a subsequent study by the same researchers showed that the Omicron BA.1 variant can persist on surfaces for even longer than the original strain. Sign in for details.

Microbiologists who placed coronavirus samples on the interior surfaces of a car, including carpeting and plastic parts, found that viral concentrations were reduced by greater than 99% within 15 minutes when the interior air was heated to 133°F (56°C), raising surface temperatures to 120°F (Unpublished study reported in The New York Times, May 30, 2020).

Don't directly refrigerate or freeze — it keeps the virus infectious

Studies with coronaviruses noted above and by others (Kampf, J Hosp Infect 2020) indicate that cold temperatures help preserve it and keep it infectious. Consequently, you should not place a recently purchased food container directly into a refrigerator or freezer and you should not "quarantine" a recently received package in a cold cellar or cold garage, as this will preserve coronavirus and could keep it infectious for days. Freezing can preserve coronavirus for years (WHO, COVID-19 Situation Report 32, 2020). The good news is that the coronavirus won't linger quite as long on surfaces and in the air in warm summer weather as it does in the winter, although this won't make much of a difference should an infected person cough near you. 

How effective are disinfectants against coronavirus?

The U.S. EPA's "List N" provides a searchable list of disinfectants that meet the agency’s criteria for use against SARS-CoV-2. Use the search box on the EPA's website to quickly look up a product by brand name or ingredient and be sure to view the "Contact Time" to see how long each disinfectant must remain wet on a surface. The list includes ready-to-use liquids, dilutable liquids, and wipes. Be aware that products on List N have not necessarily been tested specifically for effectiveness against SARS-CoV-2 but have demonstrated efficacy against a similar coronavirus or a harder to kill virus. The search results for a particular product or ingredient will indicate whether that product/ingredient has been tested against SARS-CoV-2, or viruses that are similar to or more difficult to kill than SARS-CoV-2. If you want to use a product that is not on the EPA's List N, you may also look for an EPA-registered product that lists "human coronavirus" as a target pathogen on the product label. If the product does not have an EPA registration number, the EPA has not reviewed data on whether it kills viruses such as SARS-CoV-2.

Common disinfectant ingredients
As part of the study discussed above, the Hong Kong researchers also showed that common disinfectants were effective in killing SARS-CoV-2. The virus was undetectable after 5 minutes of exposure to household bleach (i.e., sodium hypochlorite, at a concentration of 1:49 or 1:99), ethanol (70%), povidone-iodine (7.5%), chloroxylenol (0.05%), chlorhexidine (0.05%) and benzalkonium chloride (0.1%). Fifteen minutes were required for the virus to be undetectable when exposed to a hand soap solution (Chin, Lancet 2020). The researchers only checked at 5 and 15 minutes, so it is possible that less time is necessary, but as we don't know the minimum time for disinfection, it would seem prudent to allow disinfectants a few minutes on surfaces before wiping them off.

Another disinfectant is hypochlorous acid (often abbreviated as HOCL), a weak acid that can kill viruses by injuring the lipid layer of the virus cell membrane, and producing other substances that can break and render inert DNA strands within the virus. In laboratory studies, hypochlorous acid at a concentration of 0.02% was shown to inactivate viruses such as norovirus (considered a harder-to-kill virus than SARS-CoV-2) within one minute, and, at a concentration of 0.002%, within 10 minutes (Block, J Oral Maxillofac Surg 2020). It is an EPA-registered disinfectant that is expected to kill SARS-CoV-2 on hard, non-porous, surfaces given a contact time of at least 10 minutes, which is similar to the agency’s recommended contact time for regular Clorox Bleach, but longer than contact times for other bleach products, such as Clorox Fresh Scent Clorox Bleach (six minutes) or products using other disinfectant ingredients, such as Clorox Disinfecting Wipes made with quaternary ammonium (15 seconds).

Sign in as a member for details about hypochlorous acid products such as Force of Nature and Cleansmart Daily Surface Cleaner.

Be careful when using and storing chemical disinfectants

Calls to poison control centers increased sharply in March 2020 due to disinfectants (CDC, 2020). Cases have included a woman who developed difficulty breathing after mixing 10% bleach with vinegar and water to wash her produce and a child was found unresponsive after consuming ethanol-based hand sanitizer. The CDC advises that "users should always read and follow directions on the label, only use water at room temperature for dilution (unless stated otherwise on the label), avoid mixing chemical products, wear eye and skin protection, ensure adequate ventilation, and store chemicals out of the reach of children."

Hand sanitizer

The importance of proper hand hygiene in potentially reducing the spread of COVID-19 was highlighted by a study that showed that SARS-CoV-2, the virus that causes COVID-19, can survive on skin for up to 9 hours, which is longer than the 1.8 hours for a flu virus (Hirose, Clin Infect Dis 2020). Keep in mind, however, that contact transmission is not considered to be the primary method of COVID-19 transmission — virus-containing droplets in the air are the primary route, and the "infectious dose" of SARS-CoV-2 needed to spread COVID-19 infection remains unclear.

When soap and water are not available, the CDC advises using hand sanitizer containing at least 60% alcohol (typically hand sanitizers contain alcohol in the form of ethanol or isopropyl). Sign in to find out how hand sanitizers or disinfectant hand wipes compare to washing hands with soap and water to remove microbes without causing skin dryness and redness.

Be aware that alcohol-based hand sanitizers can cause eye injury and even blindness if they come in direct contact with the eye. This may occur, for example, when dispensers are placed at or above eye level, allowing sanitizer to directly squirt, or reflect off the hands, into the eye, and has been reported in children (Yangzes, JAMA Ophthalmol 2021).

The CDC also notes that benzalkonium chloride, an ingredient in some hand sanitizers, has "less reliable activity against certain bacteria and viruses than either of the alcohols." A review of studies suggests that most alcohol-based hand sanitizers are effective at inactivating coronaviruses in general, although tests of their effects on SARS-CoV-2, the coronavirus that causes COVID-19, were not included (Golin, Am J Infect Control 2020). The researchers also emphasized the importance of using an adequate amount of hand sanitizer, which a study among adults found should be at least ½ teaspoon or more to get complete coverage, but one pump from a dispenser provides only about half of this amount: Two pumps are needed to achieve better coverage. Hand sanitizers used in the study included Purell Advanced Instant Hand Sanitizer and Purell Advanced Instant Hand Sanitizer Foam, each containing 70% ethanol (Kampf, BMC Infect Dis 2013).

Be aware that the FDA has warned consumers not to use a variety of hand sanitizers that have been found to contain methanol. Methanol is toxic and can cause serious illness or death when absorbed through the skin or ingested. See the FDA's page that lists the warnings to-date. Also, fifteen brands of hand sanitizer sold in the U.S. have been found to contain potentially dangerous levels of benzene, a known carcinogen. Sign in to see the list.

Disinfecting wipes

If you use a disinfecting wipe on a surface that may come in contact with food or be placed in the mouth (like a baby bottle), be sure to rinse the surface with water and dry after wiping. A Clorox spokesperson told ConsumerLab that "Clorox Disinfecting Wipes can disinfect plastic packaging that is non-porous. Packaging should not have any holes that would allow the disinfectant to make direct contact with food. The wipes should never be used directly on food and should not be used on paper or cardboard packaging." As some consumers have wondered if the wipes can be used on microwaveable "steam" bags (as for steaming vegetables), it would seem that the wipes can be used on the front and back surfaces but perhaps not at the ends and seams where steam vents are placed.

Clorox wipes have a shelf life of one year from the date of manufacture, and Lysol indicates two years for its wipes.