The coronavirus is primarily a respiratory illness, and it typically spreads via airborne droplets from an infected person's coughs or sneezes.

Viral particles can survive for a time on surfaces, but the coronavirus' life span on surfaces depends on various factors like temperature and humidity.

New research suggests the coronavirus can last three hours to seven days on surfaces, depending on the material.

Here are some best practices for disinfecting common surfaces.

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The new coronavirus causes a respiratory illness, so it typically spreads via airborne droplets. When an infected person coughs or sneezes, droplets carrying viral particles can land on someone else's nose or mouth or get inhaled.

But a person can also get the coronavirus if they touch a surface or object that has viral particles on it and then touch their mouth, nose, or eyes. The life span of the virus on a surface — a subway pole, a stairwell banister, or even money — depends on many factors, including the surrounding temperature, humidity, and type of surface.

A study published April 2 in the journal The Lancet found that the virus lasted longest — up to seven days — on stainless steel, plastic, and surgical masks.

How long the coronavirus could survive on surfaces

The researchers behind the new study tested the virus' life span in a 71-degree-Fahrenheit room at 65% relative humidity. After three hours, the virus had disappeared from printing and tissue paper. It took two days for it to leave wood and cloth fabric. After four days, it was no longer detectable on glass or paper money. It lasted the longest, seven days, on stainless steel and plastic.

Strikingly, the authors wrote, of all the materials they tested, the coronavirus lasted longest on the outer layer of a surgical mask. On day seven of the investigation, the virus was still present on the outward-facing side of the mask.

Workers spraying disinfectant as a precaution against the new coronavirus at a department store in Seoul, South Korea, on March 2. Lee Jin-man/Associated Press

The study followed earlier research that also tested the coronavirus' life span on household surfaces. The prior study, published March 17 in the New England Journal of Medicine, suggested the virus could live up to four hours on copper, up to a day on cardboard, and up to three days on plastic and stainless steel. That was in a 70-degree-Fahrenheit room at 40% relative humidity.

The researchers compared the new coronavirus' life span on surfaces to that of the SARS coronavirus. They found that both coronaviruses lived the longest on stainless steel and polypropylene, a type of plastic used in everything from toys to car parts. Both viruses lasted up to three days on plastic, and the new coronavirus lasted up to three days on steel.

On cardboard, however, the new coronavirus lasted 24 hours, or three times the eight hours that SARS did.

Smooth surfaces are better for the coronavirus

Another study, published March 1 in the Journal of Hospital Infection, looked at the life spans of other coronaviruses found in humans on various surfaces. The SARS coronavirus, at a temperature of 68 degrees Fahrenheit (20 degrees Celsius), lasted for two days on steel, four days on wood and glass, and five days on metal, plastic, and ceramics. (The researchers also found that one strain of SARS lasted up to nine days on a plastic surface at room temperature.)

SARS survived for two to eight hours on aluminum and for less than eight hours on latex.

According to Rachel Graham, an epidemiologist at the University of North Carolina, smooth, nonporous surfaces like doorknobs and tabletops are better at carrying viruses in general. Porous surfaces — like money, hair, and cloth fabric — don't allow viruses to survive as long because the small spaces or holes in them can trap the virus and prevent its transfer, Graham told Business Insider.

"Coins will transmit a virus better than cash, but this shouldn't be a huge concern," she said. "Basic rule of thumb should be to consider money dirty anyway, because it is. It goes through too many hands not to be."

A man with coins collected from the Trevi Fountain in Rome. Marco Di Lauro/Getty

Your smartphone, with all its glass and aluminum, can also carry viral particles.

Graham recommended disinfecting your phone, "particularly if it travels to the bathroom with you."

The surrounding temperature makes a big difference

The Journal of Hospital Infection study also found that spikes in temperature made a difference in the life spans of coronaviruses. An 18-degree-Fahrenheit jump, from 68 degrees to 86 degrees, decreased how long SARS lasted on steel surfaces by at least half.

The Lancet study found a similar link between the virus' life span and the surrounding temperature. At 4 degrees Celsius, or 39 degrees Fahrenheit, the virus lasted up to two weeks in a test tube. When the temperature was turned up to 37 degrees Celsius, or 99 degrees Fahrenheit, that life span dropped to one day.

That's because some coronaviruses, including this new one, have a viral envelope: a fat layer that protects viral particles when traveling from person to person in the air. That sheath can dry out, however, killing the virus. So higher humidity, moderate temperatures, low wind, and a solid surface are all good for a coronavirus' survival, Graham said.

A volunteer offering hand sanitizer to passengers who recently arrived in Hong Kong from mainland China on February 4. Willie Siau/SOPA Images/LightRocket via Getty Images

This also explains why respiratory viruses are typically seasonal: Cooler temperatures help harden the protective gel-like coating that surrounds the particles.

How to disinfect surfaces

The authors of the Journal of Hospital Infection study noted that human coronaviruses could be "efficiently inactivated" on surfaces within one minute if they're cleaned with solutions containing 62% to 71% ethanol alcohol, 0.5% hydrogen peroxide, or 0.1% sodium hypochlorite.

"We expect a similar effect against the SARS-CoV-2," they added, using the formal name for the novel coronavirus.

A member of the medical team spraying disinfectant to sanitize bathrooms in a shrine in Iran on February 27. WANA (West Asia News Agency) via Reuters

Graham said these surface disinfectants could even work within 15 seconds.

"To get the kill rates advertised on the packaging, though, that usually involves waiting for several minutes — between five minutes and six minutes," she added, though that duration is probably essential only if you're cleaning a surface in an area where someone's infected.

Similarly, the recent Lancet study submerged a concentrated virus sample in household bleach, ethanol at 70% concentration, and other disinfectants; the results suggested they all killed the coronavirus within five minutes at room temperature. Hand soap, however, took 15 minutes.

Graham said the important thing when disinfecting a surface was getting the potential infectious dose of the virus below a level that would cause disease.

"Most commercial products labeled 'disinfectants' talk about a 99.9% kill rate," she said — that should bring the dose below the threshold that would make people ill. But alcohol-based hand sanitizer is not ideal for disinfecting hard surfaces because the alcohol content is not high enough.

Hand sanitizer is meant to lower how much of the infection is on your hands "without stripping your skin of all its oils and moisture," Graham said. "Surface disinfectants — like Lysol, bleach — are better for surfaces."

Stop touching your face, and wash your hands

Graham emphasized the importance of washing your hands and not touching your face — those are the best ways to minimize your chance of picking up the coronavirus from surfaces.

The study in the Journal of Hospital Infection concluded that if a person spent five seconds touching a surface where the influenza A virus lives, 32% of the virus living on that surface could transfer to their hands.

A man on the subway in the Queens borough of New York City on February 2. Nick Zieminski/Reuters

"If you're about to eat, fix your makeup, play with the baby, etc., wash your hands," she said.

She also suggested washing your hair if it gets sneezed on, even though the virus doesn't last very long on it.

Of course, the coronavirus can't infect you through your hands, so if you never touch your eyes, nose, mouth, you can avoid infection.

A currency trader at KEB Hana Bank in Seoul on March 5. Ahn Young-joon/AP

But that's easier said than done.

"Most humans touch their faces several hundreds of times per day, so it's still best to be aware of how clean your hands are," Graham said.