How effective are homemade face masks?

This time last year, none of us could have predicted that wearing a face mask would be normal in the western world.

The first time I saw a New Zealander wearing one in public was back in March, a couple of days before our Prime Minister, Jacinda Ardern, announced that we would all hole ourselves in.

I went to the supermarket. Staff were pushing trolleys around, complaining that they couldn't fill people's delivery orders because they were out of gloves, disinfectant, masks, and hand sanitiser. Everyone was quiet. The scary new threat that had emerged in our country only days before had made everyone uneasy.

Funnily enough, there always seemed to be toilet paper left on the shelves. Perhaps because there are so many soft, fluffy cats in New Zealand? (image source)

In the midst of the craziness stood a woman clad in blue, wearing gloves and a facemask, her arms open wide as she told everyone she saw to put a mask on. She was removed by security, but the fact that she had felt the need to tell everyone to protect themselves against the virus was a sign of things to come.

Fast-forward, into lockdown. Suddenly, face masks were all the fashion. The streets were silent, other than a few zombie-like solitary locals who were out for the brief daily exercise they were permitted. Teddy bears were pressed up against windows, cable tied to letter boxes, or nailed to fences in an attempt to cheer up children and remind everyone that we were in this together. Nobody talked. Nobody left the house unless it was absolutely necessary.

The teddy bears joined us in our suffering. Truly, we were in this together. (Photo credit: Sarah Cragg)

Visiting the supermarket was an eerie and hazardous experience. We needed food, but everything had been touched by potentially infected people. While the vast majority of shoppers respected the two-metre rule, a few whooshed past with a few centimetres to spare, and some got right up in my face.

They were usually wearing face masks, as though they were armour.

Staff, too, appeared to feel immune to the virus as they silently busied themselves in the aisles. They made little or no attempt to maintain social distancing, and there was even someone stationed in the doorway motioning people in - to get through the door, you had to close the distance between you and them. That person was in contact with hundreds of people every day. But it was okay, because they had a small cotton triangle hanging from their ears.

Or was it? Various research shows that face masks help protect people from COVID-19. However, some research shows that wearing a non-surgical mask does not protect the wearer from the virus. If everyone wears masks, the virus will be unable to transfer easily from person to person. But wearing a mask does not make you immune.

Masks have now become commonplace. Our species tends to make creative, personalised solutions to problems, so of course you can buy patterned masks made from cloth. However, cloth masks were not tested for efficacy until recently.

Homemade masks are fashionable and fabulous. But are they effective?

A team of scientists from the UK and USA have been spending the last few months modelling the efficacy of different mask materials as shields against COVID-19. Their paper shows that most homemade mask materials were ineffective as barriers against the virus when compared with rated or surgical masks, although they were generally a little more effective than wearing no mask at all.

The nonchalant scarf wraparound was shown to be the least effective face covering for protection against COVID-19, with up to 44% protection against virus particles. Unsurprisingly, the mighty FFP3 was hands-down the most effective, with up to 99% protection against virus particles. But of the homemade mask materials, vacuum cleaner bags stood out as the most effective (up to 83% protection).

The amount of protection a mask can give someone varies based on how it is worn. Remember this cartoon?

The efficacy of a mask also depends on the amount of time it is worn while exposed to virus-containing droplets. The above protection percentages are based on a 30-second exposure to droplets; after 20 minutes, efficacy dropped to 94% (FFP3), 24% (scarf), and 58% (vacuum cleaner bag).

So those supermarket staff and shoppers, wearing their cloth masks, in amongst people all day every day...they still should have maintained their social distancing. A mask is not a substitute for keeping two metres away from everyone.

And you may look cool with a scarf wrapped around your face, but a much better alternative would be a vacuum cleaner bag inserted into a cotton or netting mask.

I must point out the limitations of this research. As important as COVID-19 research is, there are still codes of ethics to follow when conducting it. For some reason, the scientists did not think it proper to leave dozens of healthy people in a room with a sick person for up to 20 minutes, wearing pillowcases, scarves, surgical masks or no protection at all, and then see who got sick. The results are all based on modelling, using known figures of respiratory droplet size, virus particle size, mask filtering efficacy, respiration rate, and infection probabilities and rates. This modelling is pretty advanced and probably very accurate, but the real world contains lots of tiny factors and statistics that cannot all be incorporated into models. So this research is the best thing we have to go on at the moment, but it is not a complete picture.

Be safe, and wear your mask (or vacuum cleaner bag), and distance yourself from others, and stay home where you can. These are turbulent and troubling times, but they will pass, and our scientific knowledge and ability to care for each other will get us through.