Discourse regarding personal protective equipment (PPE, including cloth face masks) was a large part of COVID-19 discussion on social media in early April 2020, including a viral Facebook post that repeats purported advice to sterilize cloth masks by microwaving them between uses:
The brief post attributed the recommendation to the president of Meharry Medical College in Nashville:
If wearing a fabric mask, Meharry Medical president just stated to place mask in ziplock bag and heat in microwave for 2-3 minutes to sanitize after each use.
As is the case with most text-based Facebook status updates, the claim appeared without specific citations or links indicating the advice was authentic or correctly described.
A quick search led to an April 6 2020 WMOT article (“Nashville Coronavirus Task Force member calls for mask use in public.”) As suggested, the information had to do with new COVID-19 recommendations involving the use of masks in public spaces; as of early April 2020, multiple media reports advised people in all states to wear personal protective equipment if possible.
Disposable face masks (as well as N95 respirators) were in notoriously short shrift, meaning that most non-medical workers lacked access to any sort of commercial face mask. Consequently, people began fabricating their own out of household materials such as T-shirts, bandannas or scarves, and dish towels or fabric scraps.
WMOT’s article referenced an April 3 2020 press conference, and it highlighted recommendations that people wear cloth face masks:
A member of Nashville’s Coronavirus Task Force has called on Metro residents to begin wearing masks in public.
Meharry Medical College CEO Dr. James Hildreth made the suggestion [on April 3 2020] during Nashville’s daily pandemic press briefing. Dr. Hildreth noted the latest research suggests infected individuals can spread the illness before they even show symptoms.
Hildreth stressed that high-quality manufactured masks need to be reserved for front line medical staff. He [recommended] that individuals using [homemade] masks  wash their hands each time they take the mask off. He also stressed the need to sterilize the mask regularly.
An April 3 2020 YouTube video, titled “Mayor John Cooper News Conference,” was embedded in the story. Just before the 12:30 mark, Meharry President and CEO James E.K. Hildreth Sr., Ph.D., M.D. began speaking.
Hildreth first spoke about visible signs of infection with respect to other illnesses, explaining that there were, unfortunately, no visible signs for COVID-19 infection in the general population. He subsequently indicated there was a “reason why” citizens of other countries are known to wear masks, and people in those countries have lower rates of COVID-19 transmission.
Hildreth stated that if everyone wore masks, the chain of transmission of COVID-19 would decrease across the board. He emphasized it was necessary to reserve commercial PPE like disposable face masks for medical professionals and those on the front line. Then he added that if you are following recommendations, there are a couple of things “you really need to know,” explaining:
There’s a national urgency — and I’m gonna repeat this — that the PPE must be reserved for healthcare providers and those on the front line. So many people have resorted to making homemade masks out of bandanas and other kinds of materials … there are a couple of things you really need to know if you’re doing this:
If the mask has served its purpose, there’s every possibility it’s contaminated on the outer surface. What that means is that you should do two things: wash your hands when you take it off, and sterilize it or sanitize it if you’re gonna use it repeatedly.
If possible, wash it in soap and water. And if it’s made out of cloth or has no metal staples in it, you can do what I do: stick it in a plastic bag, and microwave it for two or three minutes at the highest setting.
Numerous studies show that many, many types of bacteria, fungus, and viruses are killed by microwave radiation. You must make sure that your improvised device is compatible with microwaving, and if it is, stick it in a plastic bag and zap it for two or three minutes at the highest setting.
I want to emphasize as you heard earlier that our best strategy still for controlling the virus is to stay at home. My heart breaks every time I hear a new story about a nursing home where the people have gotten infected.
The virus is not floating in the air … someone delivered the virus to that facility, that’s how it started.
Someone was a vector. Please stay at home — comply with the order to stay at home. Only go out when you absolutely have to, and if you have to go out, please cover your face to avoid becoming a vector.
Additional information about sterilizing cloth face masks and PPE from the Centers for Disease Control and Prevention is available here. That guidance also included instructions for fabricating a coronavirus mask at home.
The Facebook post accurately identified both the speaker — Meharry Medical College president and chief executive officer James Hildreth — and the advice. Hildreth made the recommendation on April 3 2020 (the day the post appeared), and he included some important caveats about correct use of improvised face masks to avoid contracting or transmitting COVID-19. Hildreth emphasized the necessity of handling masks as if contaminated, and also checking the mask for any metal parts before microwaving them. In the case of compatible masks, Hildreth suggested two to three minutes of microwaving them “at the highest setting.”