MARTIN DE RUYTER/STUFF
Dr Richard Everts, Nelson Marlborough Health infectious disease specialist, hangs face masks out to dry after washing them.
Disposable medical face masks can be washed up to 10 times and still offer better protection than homemade fabric masks, a Nelson-based infectious disease expert has found.
Dr Richard Everts, an infectious disease specialist and microbiologist for Nelson Bays Primary Health and Nelson Marlborough Health, carried out a research project on masks with a team of helpers.
Everts decided to study how long to reuse disposable masks for after working in Vanuatu when Covid-19 started to spread in China.
“I realised we didn’t have enough masks in Vanuatu,” he said. “As a developing country, they were never going to be able to throw their masks out.”
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The research team took three brands of commercially available disposable polypropylene masks that met international standards and washed them in eight different ways.
They found that the disposable masks, which started off with 95 per cent efficacy, could be washed and dried 10 times and still work well, Everts said.
The best way was simply washing in warm tap water for 10 seconds while gently massaging them, with no detergent, and then drying them to kill the bacteria, for reuse. This reduced the efficacy down to 80 per cent, which Everts said was still good. Two brands were still close to 90 per cent after 10 washes.
Soaking masks in hot boiled water for five minutes had a similar effect.
Everts said each time they tried washing masks with soap or detergent, using bleach or washing the disposable masks in a washing machine the efficacy reduced to about 50 per cent.
Once masks were worn for three or four hours they needed to be washed because they would start getting dirty, with saliva, mucus and bacteria, he said.
Disposable masks offered better protection than cloth masks. The best disposable masks would stop 95 per cent of all bugs, while only a few of the best commercially available cloth masks get above 90 per cent efficacy. Most were 70 per cent, Everts said.
“Once people have made themselves at home, those will go anywhere from five to 20 per cent, so they’re not stopping many viruses at all.”
Some people had sewn in three to four layers of material, which brought a cloth mask’s filtration efficacy up to about 30 or 40 per cent, he said, although it was then often harder to breathe.
Filtration efficacy also reduced with cloth masks after a few washes, he said.
However, because it was important face masks fit the wearer well, and because everybody’s head shape differed, for some people a homemade mask was the best option, Everts said.
“They just need to be warned that after a few washes they are not very good any more.”
For people more vulnerable to Covid-19 and those with compromised immune systems, an N95 mask, with its high level of filtration and fit, was a good choice, Everts said.
“They are the kind of people I recommend invest in a $5 mask, rather than a 30 cent mask.”