Touching any surface suddenly seemed dangerous at the beginning of the coronavirus crisis, but experts now worry less about COVID-19 spreading this way.
Surface transmission is "not thought to be a common way" that the illness is spread, though it's possible a person could get sick by touching an object contaminated with the virus and then touching his or her face, the Centers for Disease Control and Prevention noted.
COVID-19 most commonly spreads during close contact with a person who is sick, but experts say people should remain vigilant about washing their hands, focusing on that more than wiping down delivered packages, mail or other objects with disinfectant.
How long does coronavirus live on surfaces?
Coronaviruses found on surfaces and objects "naturally die within hours to days," with warmer temperatures and exposure to sunlight reducing that time, according to the CDC.
But in the fall of 2020, Australian researchers reported the virus that causes COVID-19 can survive on paper money, glass and stainless steel for up to four weeks, much longer than the flu virus.
At about room temperature, the study found the virus "was extremely robust, surviving for 28 days on smooth surfaces such as glass found on mobile phone screens and plastic banknotes."
The research involved drying virus in "artificial mucus" on different surfaces and at concentrations similar to those reported in samples from infected patients. The experiments were done in the dark to remove the effect of ultraviolet light, which can quickly inactivate the virus.
A previous study, published in a letter to The New England Journal of Medicine in April 2020, found the virus could be detected for up to four hours on copper, up to 24 hours on cardboard and up to two to three days on plastic and stainless steel.
Critics have said studies often don't represent real-life conditions and situations, with one expert calling the chance of transmission through inanimate surfaces "very small" and only when an infected person coughs or sneezes on a surface, and someone else touches it within one or two hours afterwards.
"I do not disagree with erring on the side of caution, but this can go to extremes not justified by the data," Emanuel Goldman, professor of microbiology, biochemistry and molecular genetics at New Jersey Medical School, wrote in The Lancet in the summer of 2020.
Periodically disinfecting surfaces and use of gloves are reasonable precautions, especially in hospitals, he noted, while warning against "excesses that become counterproductive." Goldman has since also stopped wearing gloves.
Previously published studies have indicated coronaviruses in general — not specifically the new one — can last up to nine days on surfaces depending on the surface type, the heat, the humidity, exposure to sunlight and other factors, said Joseph Fair, a virologist, epidemiologist and NBC News Science contributor.
“Coronaviruses have been with us for millions of years — not this one, but other coronaviruses,” Fair told TODAY.
How does that compare to other germs?
The flu virus can stay active on some surfaces for up to 48 hours, according to the CDC.
The Ebola virus can survive on doorknobs and countertops for several hours.
The norovirus can survive up to four weeks on surfaces, said Charles Gerba, a professor of microbiology and immunology at The University of Arizona.
Some bacteria can last much longer, Fair said.
What affects how long the coronavirus stays active?
Fair called sunlight “nature’s greatest disinfectant” because the ultraviolet light inactivates bacteria and viruses.
Higher heat and humidity, on the other hand, will help it to stay active longer, he noted.
Disinfecting surfaces can kill the virus. More on that below.
Does the type of surface make a difference?
Yes, the less porous a surface, the more virus you will get on your hands when you touch it, Gerba said.
“You will pick up on your finger 70% of the viruses on stainless steel surfaces versus only 1% from a cloth surface or money,” he noted.
That being said, Fair advised people to avoid handling cash, which he called “one of the most filthy things in our society, period.” Paper money is made of cotton, an absorbable surface that can get wet.
Which surfaces are potentially the most infectious?
Any that are touched the most often, Fair said. That includes bathroom faucet handles, doorknobs, elevator buttons, hand rails and touchscreens on phones, tablets, and ATMs.
They’re the dirtiest surfaces we come into contact with because so many people touch them.
What kills viruses?
Common cleaners with either bleach or alcohol as their active ingredient inactivate infectious viruses, Fair said.
Coronaviruses are fairly sensitive to most disinfectants, including bleach, hydrogen peroxide and quaternary ammonium compounds, Gerba added. If the label says the cleaner will kill the influenza virus or norovirus, it will work against coronaviruses, too.
“I would use disinfecting wipes because then you use the right dose of disinfectant and you usually let it dry so you get the right contact time for the disinfectant to work,” he noted.