Wash your mask daily: the ultimate guide to face coverings

By Linda Geddes Science correspondent

We hook them on to our faces, laugh, sneeze and sputter into them, then crumple them into our bags or pockets only to retrieve them and do it all again. Yet despite official advice that we should be wearing a fresh face covering each time we enter an enclosed public space, a YouGov poll revealed many people are going several wears between washes – and 15% of Brits don’t wash their reusable masks at all. Similarly, more than half of those opting for disposable masks are rewearing them – 7% of them indefinitely so.

Face coverings are designed to catch the respiratory droplets we emit from our mouths and noses, but given that they’re our own respiratory droplets, is this really so bad? We examine the evidence.

How contaminated do face masks get, and with what sorts of microbes?

If you were to swab your used face covering and grow the microorganisms in a petri dish, you would find a variety of bacteria, viruses and fungi. “Most are likely to be harmless – you would get something similar if you sampled your hands, nose, mouth or many other parts of your body,” says Prof Cath Noakes, an expert in airborne disease transmission at the University of Leeds. However, combined with the friction and humidity associated with prolonged mask-wearing, this microbial menagerie could trigger outbreaks of “maskne”.

Maskne: what is it?

Maskne is an umbrella term coined to cover all manner of facial rashes associated with mask-wearing including acne, says Dr Thivi Maruthappu, a consultant dermatologist at Highgate hospital and spokesperson for the British Skin Foundation. “As masks can be a vector for bacteria, fungi and viruses, I would recommend washing your mask on a daily basis if you’re wearing it every day.” Soft fabrics such as cotton are less likely to cause friction than synthetic fibres like polyester, she adds.

What’s the risk of catching Covid-19 from a dirty mask?

If you had Covid-19, then your face covering would be heavily contaminated with coronavirus, as well as other bugs. Your mask would pose a risk to others if they handled it, so you should never share masks or touch someone else’s without thoroughly washing your hands.

Other people’s exhalations are a different matter. A 2019 study of healthcare workers identified various respiratory viruses on the outside of their masks, including influenza and adenovirus, a cause of the common cold. Although there is currently no data proving that such external contamination increases Covid-19 risk, “it theoretically could if you touched the mask and then touched your nose or eyes,” says Noakes.

So how often should I be washing my mask?

Ideally, after each time you wear it. “It is possible to get a mask contaminated after daily wear,” says Prof Raina MacIntyre, an infectious disease researcher at the University of New South Wales in Sydney. “We tested this and found virus on the inside and outside of masks, both surgical and cloth.”

Frequent washing is particularly important if you’re coming into contact with vulnerable individuals, says Prof William Ristenpart, a chemical engineer at the University of California, Davis. He recently discovered that the influenza virus could travel on contaminated dust particles, released by rubbing a contaminated tissue, say. In a separate study, he showed that dust was ejected from fabric masks during normal wear: “You can imagine if someone is infected and they are wearing a cotton fabric mask that is heavily contaminated, it’s possible that those particles could carry the virus,” he says. “Of course, you can’t wash it every 20 minutes, but every five or six days is way too long.”

How should I be washing it?

A hot wash is best, although masks can go in with your normal laundry. “Washing must be done in water that is at least 60C, with soap,” says MacIntyre. She previously conducted a trial of cloth masks among Vietnamese healthcare workers and found that, compared with surgical masks, not only did they not protect the staff, they may have increased their risk of illness. Further analysis revealed it was not the masks, per se, that were the problem, but the fact they were often washed by hand.

“The healthcare workers whose cloth masks were washed in the hospital laundry were as well protected as surgical mask users,” says MacIntyre. “Hand-washing in cold or lukewarm water is inadequate.”

Mask should also be fully dry before being worn. “Damp or moist fabric masks can be more porous and therefore less efficacious,” says Maruthappu.

What if I only wear my mask for 10 minutes, put it in my bag, then pull it out again later, or the next day?

“If done carefully and safely it should be OK,” says MacIntyre. “You must sanitise your hands first, remove the face piece [by] touching only the straps or ear loops, and put it in a ziplock bag. It can be put on again after sanitising the hands and again, not touching the face piece.”

The more times you handle your face covering without washing it or replacing it, the greater the risk will be.

Why do I need a separate container for my mask?

Because handbags and pockets, often home to keys and unwashed hands, could be dirty. There’s also a small risk that your mask may contaminate other items. “I would always recommend treating the face covering as if it is contaminated,” says Noakes. “And you would want to regularly wash or replace the container, as that would get contaminated too.”

Could I spray my mask with alcohol or disinfectant instead of washing it?

Sensible as this might sound, you would then risk inhaling chemicals from the disinfectant spray. “Also, remember that washing it is not just to remove any coronavirus, it is also to remove all the other microbes, sweat and snot from your face covering,” says Noakes. “A spray will not do this: just like your underwear, you need to wash your face covering.”

My mask contains a filter. How often should I be changing this?

As often as you should be washing or changing your mask. “I think it would be a good idea to assume that the filter gets contaminated at the same rate as the mask itself,” says Noakes.