A User’s Guide to Face Masks

Medical masks and N95 masks should be saved for medical workers, but if you have a medical mask, you should know that it was designed for one-time use. However a number of scientists, led by a group at Stanford University, are studying the best way to sanitize masks to extend the life of the personal protective equipment used by medical workers during the current shortage.

The problem is that washing or sanitizing a medical mask will degrade it, making it less effective. Scientists have found that using UV light, heat and humidity or a hydrogen peroxide vapor could work, but the methods are developed for use in hospitals with special equipment and are not for home use.

“I would be wary of putting them in the oven because of the potential to reach too high a temperature and melt the plastic fibers, thus damaging the mask,” said Linsey Marr, a leading aerosol scientist at the University of Virginia who has been studying ways to extend the life of medical masks. “Studies on other viruses show inactivation at about 150 degrees Fahrenheit, which is lower than many ovens can go. But that’s with high humidity, and the humidity makes a big difference. If you have an oven that can hit 150 degrees and you put a pan of water in there, this could be effective, but nobody has tested the method on this specific virus.”

If you have multiple masks, the best strategy is to rotate use of the masks over several days, which gives time for the virus to die. For medical workers, one strategy is to keep a set of five masks, so they can wear a new mask every day and return to the first mask on the sixth day.

“The safest thing to do might be to put the mask somewhere safely out of reach,” said Dr. Marr. “Over a few days, the viruses should decay. In fact, studies have found that viruses usually decay faster on fabric and other porous materials than on hard materials like steel or plastic.”

It’s much easier to clean a fabric mask than a medical mask. The C.D.C. says fabric masks should be “washed routinely.” The mask experts I spoke with wash theirs daily in a machine or a sink, just using regular laundry soap. You can use the dryer or let it air dry. Although it’s not necessary, you can also go over it with a hot iron for a full assault on any germs that might remain.

Just as with a medical mask, chemicals like bleach or hydrogen peroxide will begin to degrade the fabric fibers, making the mask less effective. Dr. Marr notes that a virus can’t replicate outside the body, and if virus particles have been trapped by the mask, they are pretty well stuck there and will decay or be removed during washing.

“Washing with soap and water should work,” Dr. Marr said. “I throw my cloth mask in the washing machine with the rest of the laundry and dry it on low heat. I would avoid bleach because we know that can degrade fibers. The important thing is to avoid damaging the fibers in the mask.”

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