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March 16, 2020

Why soap is (still) the best defense against the coronavirus

Daily Briefing

    It turns out, washing your hands thoroughly with soap and water is best way to protect against the coronavirus. Buy why? Vox's Brian Resnick asked Palli Thordarson, a chemistry professor at the University of New South Wales, to explain the virus-killing powers of soap.

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    About the pandemic

    Reports of the new coronavirus first surfaced in early December 2019 in Wuhan, China. As of Friday morning, officials reported more than 135,400 cases of COVID-19, the disease caused by the virus, globally.

    The United States saw its first COVID-19 case in late January, and since then cases have spiked. As of Friday morning, state and federal officials had reported 1,663 confirmed or presumed positive cases of COVID-19 in the United States, up from 231 last Friday. So far, 41 U.S. deaths have been linked to the new coronavirus.  

    Why soap is always better

    CDC and public health experts have said the most effective way to protect against the new coronavirus is to wash your hand thoroughly with soap and avoid touching your face. In the absence of soap, CDC recommends using hand sanitizer containing at least 60% alcohol.

    But according to CDC, your first choice should always be soap. When you wash your hands with soap and water, you're not only washing the virus particles off your hands, you're also "annihilating the viruses, [and] rendering them harmless," Resnick writes.

    Thordarson explained that chemists call soap "amphiphiles," which are molecules with a dual nature.

    One end of the molecule is attracted to water and repelled by fats and proteins, while the other end of repels water but attracts fats and proteins. "When you buy a conventional soap, it consists of a mixture of these amphiphiles," Thordarson said.

    The genetic makeup of coronaviruses, Resnick writes, consists of encoded RNA surrounded by a layer of fat and protein, making the viruses the "exact type of thing soap loves to annihilate."  

    Soap acts "almost like a crowbar" for the virus, Thordarson explained. One end of the soap molecule attracts to the virus's fat and protein outer layer and breaks it apart, allowing the virus to be washed away down the drain.

    "You pull the virus apart, you make it soluble in water, and it disintegrates," Thordarson said.  

    But this process can take a while to happen, which is why people should wash their hands for at least 20 seconds. "You do need a bit of time for all the soap to interact back and forth with the virus particle," Thordarson said.

    Hand sanitizer works in a similar way, but you need a very high concentration of alcohol to have the same outcome, according to Thordarson. This is why CDC recommends people use sanitizers with at least 60% alcohol, and only if soap and water are not available.

    While convenient, sanitizer can also "fail in un-ideal situations," according to Resnick. "If your hands are wet or sweaty when you use the sanitizer, that can dilute it and diminish its effectiveness. Also, sanitizer doesn't clean your hands of sticky grease to which viruses can also adhere."

    Soap, on the other hand, "doesn't really fail easily," Thordarson said.

    Research also shows the type of soap isn't as important. "Soap—all sorts of it: liquid, solid, honeysuckle-scented," is always more effective than hand sanitizer, Resnick writes (Resnick, Vox, 3/11).

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