How long can you reuse your reusable face mask?
According to the WHO, 3-layered non-medical fabric masks should be worn by members of the general public under age 60 to help stem the transmission of COVID-19. It also advises that masks should be cleaned appropriately so that they are as effective as possible. But what constitutes “appropriate” cleaning?
A quick internet search reveals that many media sources recommend washing masks daily, either in a washing machine in hot water and detergent or by soaking in a bleach solution. The mask should be dried at high temperatures in a dryer or air-dried in the sun. What experts and media sources are largely silent on is how many times you can rewash and wear your cloth masks.
I decided to wash a face mask 40 times to see how long it would last before losing effectiveness. I modelled my experiment after the “Bill Nye candle test.” In his test, the beloved scientist attempts to blow out a candle one foot away while wearing a variety of masks. In my experiment, I assumed that if the candle is blown out or even flickers significantly, then the mask must be ineffective in preventing the flow of air, and by extension, virus particles.
First, I placed the candle on a flat, non-flammable surface — safety first, as Bill Nye taught me. Then, I donned a brand-new 3-layer cloth mask. Then, the fun part — I blew air as hard as I could at a candle from 10cm, 20cm, and 30cm away. Each time, I observed and recorded whether the candle flickered or was extinguished. Then — the less fun part — I washed the mask 10 times by hand using a bleach detergent, repeated the test, rewashed it 10 times, and so forth. Wash, test, repeat.
What I discovered was that the effectiveness of the mask significantly declined after 30 washes. Whereas the mask originally prevented the flame from flickering from a distance of 20cm away, after 10 washes, the flame began to flicker. By 20 washes, the flame blew out from 20cm away.
By viewing the mask under 2000x magnification, I confirmed that after 10 washes, the mask’s weave was noticeably looser, and the cotton fibres had started to unravel. This unravelling worsened with continued washing. By 40 washes, the fibres had become significantly separated, and the mask had become least effective for blocking airflow to the candle (I was able to blow out the candle from 30cm away!). I also noticed that the mask became looser due to the stretching of the ear loops, allowing more air to escape through the top and sides. Unsurprisingly, studies have found that there is significant damage to cotton fabrics after 50 washes using a bleach detergent.
Images of cloth mask fibres (2000x magnification)
The coronavirus is transmitted through microscopic, highly contagious airborne particles. The new variants are even more infectious. This means that the effectiveness of commonly used masks is critical in preventing the spread of COVID-19.
I surveyed 100 people to find out what people believe about washing masks. Most people wash their reusable face masks regularly (almost 30% reported washing after every use, and 15% washed daily). However, over 50% thought (incorrectly) that a reusable mask can be washed daily for over a month with no loss in effectiveness.
The reality is that washing a 3-layer reusable cotton mask over 40 times renders it ineffective. The fibres deteriorate, and gaps form in the weave. So, let’s continue to follow the advice of Bill Nye: safety first! Ensure there is a steady supply of face masks at home and a system to keep track of the number of washes. Don’t forget to discard those cloth masks after 40 washes.
