How to Clean Face Masks Against Coronavirus

A standard laundry cycle is enough to wash the coronavirus off cloth, according to the WHO and CDC.

“Because it’s an enveloped virus, it’s really susceptible to detergents,” says Rachel Graham, a virologist at the University of North Carolina at Chapel Hill. The envelope that encapsulates viruses like influenza and SARS-CoV-2 is a delicate layer of oily lipids and proteins, held together by surface tension.

Laundry detergents and soaps contain surfactants, chemicals that easily break that envelope apart by reducing surface tension, explains Joshua Santarpia, a pathologist at the University of Nebraska Medical Center in Omaha. A surfactant molecule has one end that’s attracted to oil and grease, while the other is attracted to water. The oil-loving end wedges into the coronavirus’s envelope, busting it apart. The remnants get trapped in circular pods of surfactant called micelles and are washed away in water.

“The interaction of that surfactant with the viral envelope pretty quickly destroys the ability of that virus to be infective,” Santarpia says. Potent surfactants are found in most home and commercial cleaning products.

The water temperature in the washing machine doesn’t matter as long as you use detergent. “The masks made of cotton withstand higher temperatures, so if it makes you feel better to wash it at a higher temp, go ahead and do that,” Graham says. The high, concentrated heat from a dryer offers added protection: it’s enough to kill most microorganisms.

What if I’m wearing a surgical or N95 mask?

Unlike cloth coverings, medical masks intended for single use are made of non-woven synthetic fabrics that can’t withstand a typical laundry cycle.

“If you wash them it will do a lot of damage to their filtration capability,” Santarpia says. Out of necessity, healthcare workers have been reusing N95 respirators—the dome-shaped, tight-fitting masks that are the only verified way to efficiently filter small particles like viruses. The facilities where Flinn and Santarpia work use hospital-grade disinfectants that preserve the mask’s integrity through the cleaning process.

Santarpia’s Nebraska hospital is also sanitizing masks with UV-C, a high-energy type of ultraviolet light. That allows staff to re-wear masks a handful of times, Santarpia says. Because UV-C is considered more intense and more likely to cause cancer than UV-A and UV-B, this brand of sterilization should only be conducted under expert supervision by people trained in using UV-C light, according to the CDC.

For the general public, the bottom line is, you should ideally only wear medical masks once—and if you’re going to reuse them, set them aside between uses long enough for the virus to decay.

How long is that? Scientists are still unpacking exactly how long SARS-CoV-2 lasts on surfaces, in the air, and on masks. Preliminary evidence released late last month without peer-review found traces of the coronavirus persisted for considerable time on N95 respirators.

“The take-home message is that the virus can remain infectious for several hours, potentially up to a few days, on various surfaces, including masks,” says Amandine Gamble, one of the study’s authors and an infectious disease expert at the University of California Los Angeles. She suspects the coronavirus gets trapped within a mask’s fibers, which poses a hazard until the germ spontaneously degrades over time. For this reason, the CDC advises against wearing an N95 respirator for more than 8 hours total, and unless otherwise specified by the manufacturer, those face filters should be discarded after five reuses.

But even outside of hospitals, respirators that are reused repeatedly in public could collect virus over time and increase the wearer’s own chances of accidental exposure.

“The one important thing to keep in mind is that the probability of getting infected increases with the number of viral particles encountered,” she says. “It is not an on-off process, but a gradual one.”