Question: I’ve been reading on the twitters that we can disinfect our masks by putting them in the oven and/or microwave. Any truth to that?
Answer: When it comes to sterilizing homemade and cloth face masks, CDC recommends, “A washing machine should suffice…” When it comes to sterilizing N95 masks at home, however, a washing machine is not your best bet — cleaning products will degrade the filtration efficacy. Microwaving N95s is not a good idea either; the Society of American Gastrointestinal and Endoscopic Surgeons says, “At-home microwaving is not recommended because of variable power settings, and metal portions of the masks may catch fire.” A couple of studies have come out in recent days that provide more guidance on the best way to sanitize your N95 or surgical mask at home, and ovens seem like they might work (details and caveats follow).
A couple of studies have come out in recent days that provide more guidance on the best way to sanitize your N95 or surgical mask at home. The first such study disinfected masks by — placing the mask in a paper bag (like a lunch bag); putting the paper bag in an oven safe container; preheating the oven on to 170°; and “cooking” the mask for 45 minutes. Researchers tested how well the mask filtration worked after each decontamination cycle for 10 cycles and found that “no reduction in average filtration efficacy was observed.” A second study, published three days ago, reports “We found that heat (≤85 °C [185 °F]) under various humidities was the most promising, nondestructive method for the preservation of filtration properties in meltblown fabrics as well as N95-grade respirators.” So, heating in the oven seems like a promising approach for disinfecting N95 and surgical masks. BUT (because it seems like there’s always a but!), I’d also caution that the promising results of the two studies I cited are a shift from previous evidence that had shown that decontamination using dry heat caused “substantial filter degradation.” Two studies based on lab conditions do not a strong evidence-base make. Ideally, we’d want more evidence before making a recommendation.
*Reminder, we regular civilians are supposed to save the N95s for health workers, so while supplies are short, please refrain from purchasing N95s and keep using cloth face masks.