PUBLISHED March 18, 2020

For nearly 5,000 years, humans have concocted cleaning products, yet the simple combination of soap and water remains one of the strongest weapons against infectious diseases, including the novel coronavirus. Even so, when outbreaks like COVID-19 occur and panic sets in, people rush to buy all sorts of chemical cleaners, many of which are unnecessary or ineffective against viruses.

Foam hand sanitizers are disappearing from store shelves, even though many lack the necessary amount of alcohol—at least 60 percent by volume—to kill viruses. In countries hardest hit by the novel coronavirus, photos show crews in hazmat suits spraying bleach solutions along public sidewalks or inside office buildings. Experts are dubious, however, of whether that’s necessary to neutralize the spread of the coronavirus.

Using bleach “is like using a bludgeon to swat a fly,” says Jane Greatorex, a virologist at Cambridge University. It can also corrode metal and lead to other respiratory health problems if inhaled too much over time.

“With bleach, if you put it on a surface with a lot of dirt, that [dirt] will eat up the bleach,” says Lisa Casanova, an environmental health scientist at Georgia State University. She and other experts instead recommend using milder soaps, like dish soap, to easily sanitize a surface indoors and outdoors.

To fully understand why health officials keep coming back to soap, it helps to know how the coronavirus exists outside the body, and what early research is saying about how long the virus can linger on common surfaces.

The hard surfaces made for coronavirus

The primary way people become infected with the coronavirus is from person-to-person transmission. This close contact in the form of a hug, handshake, or being in a packed public space enables infected individuals to easily spread their respiratory droplets, which are typically sneezed or coughed.

But because respiratory droplets are heavy, they typically fall to the ground easily. Depending on where they land, they could persist on a surface before being touched by a hand that carries the virus to a nose or mouth, leading to infection.

All viruses are bits of genetic code bundled inside a collection of lipids and proteins, which can include a fat-based casing known as a viral envelope. Destroying an enveloped virus takes less effort than their non-enveloped compatriots, such as the stomach-busting norovirus, which can last for months on a surface. Enveloped viruses typically survive outside of a body for only a matter of days and are considered among the easiest to kill, because once their fragile exterior is broken down, they begin to degrade.

Yet every enveloped virus is different, and scientists around the world are aggressively researching SARS-CoV-2, the official name of the new coronavirus, to understand how it stacks up. A study published Tuesday in the New England Journal of Medicine looked at how long it can be detected on various materials. Dylan Morris, an evolutionary biologist at Princeton University and a study co-author, says the mission was to investigate which surfaces found in medical settings might serve as a potential cesspool for infecting patients.

On surfaces, they found SARS-CoV-2 lasted for 24 hours on cardboard, two days on stainless steel, and three days on a type of hard plastic called polypropylene. The virus could only be detected for four hours on copper, a material that naturally breaks down bacteria and viruses. The study also revealed the novel coronavirus and its cousin SARS, which caused a major outbreak in 2002 and 2003, last on surfaces for similar amounts of time. (Find out how coronavirus spreads on a plane—and the safest place to sit.)

People ordering goods online to avoid crowds may conceivably come into contact with contaminated cardboard, though the U.S. Centers for Disease Control and Prevention emphasizes that surfaces are not thought to be the primary way the virus is transmitted.

Morris doesn’t want to speculate too much on everyday surfaces, but his general advice would be to carefully wash items and one’s own hands.

But their study has limitations. The team examined the virus in a highly controlled lab setting. Spaces that are commonly touched, like a stair rail or bus pole, would contain a higher amount of the virus and present a greater risk for infection. Environmental conditions can also influence how long the virus lasts. Humidity, for example, is thought to make it harder for respiratory droplets to travel through the air, and ultraviolet light is known to degrade viruses. (Will warming spring temperatures slow the coronavirus outbreak?)

The study also found the novel coronavirus could persist as aerosols—tiny airborne particles—for up to three hours, though Morris clarifies larger respiratory droplets are more likely to be infectious. Viral aerosols are primarily a concern in clinical settings where certain treatments like ventilation can produce these particles. It is unlikely that these coronavirus aerosols come into play in open-air settings or public places like supermarkets.

Wood, food

Morris’s study didn’t include commonly touched items like clothing or produce, but there is no evidence that the novel coronavirus can be transmitted via food, according to the U.S. Food and Drug Administration.

In studies of influenza viruses, porous items like clothes and wood didn’t contain the virus for longer than four hours. That’s because these items pull moisture away from the virus and cause it to degrade.

No matter what you touch, soap and water is the best way to remove any potential coronavirus from your hands before it can lead to infection. The coronavirus does not penetrate through skin because your outermost layer is slightly acidic, which prevents most pathogens from entering the body, explains Greatorex.

Soap works so effectively because its chemistry pries open the coronavirus’s exterior envelope and cause it to degrade. These soap molecules then trap tiny fragments of the virus, which are washed away in water. Hand sanitizers work similarly by busting apart the proteins contained in a virus.

Tap water is also not a cause for concern, experts say, because any contamination would need to come via wastewater. Though the coronavirus has been found in feces, the virus has yet to actually be detected in wastewater, according to the CDC. Even if that were the case, U.S. water filtration is robust enough to kill coronaviruses, says Kyle Bibby, an environmental engineer at the University of Notre Dame.