Cloth masks: “Better than nothing” … kinda

Published April 23, 2020

‘Wearing a mask is important for flattening the coronavirus curve.’ Unfortunately, there’s as much theater in that as real science.

That’s because the weave in cloth masks is way, way, way to loose to stop most of particles of a virus. If someone is infected, the virus will sail through the pores.

An N95 mask will filter 99% of the virus. A proper medical mask (aka “surgical mask” will filter most of it. But, as a 2010 study found:

  • Sweatshirts blocked about 20-30% of virus-sized particles
  • T-shirts blocked 14%
  • Hanes brand T-shirts blocked 43-60% (the 100% cotton kind)
  • Cotton towels blocked 34-40%
  • Scarves blocked 11-27%

But cloth does stop some of the virus, you might think, and therefore a cloth mask or bandana is better than nothing. And it can reduce the chance of an infected person spreading the virus, right? On paper, yes. (Or, rather, in the lab.) Reality ain’t so simple.

The problem is threefold:

  1. The masks don’t filter very well and may increase risk-taking by giving a false sense of security.
  2. Fabric tends to retain moisture and thus can cause viral particles to ‘stick,’ turning the mask itself into a source of infection.
  3. Reusing the masks without properly cleaning them renders them all but pointless, especially if you touch them with infected hands.

So yes, using a clean cloth mask that you haven’t touched with your dirty fingers will provide better-than-nothing protection from viruses. But think of them as using gardening gloves to do electrical work: They really aren’t a great option, but if you’re very careful they can reduce your risk.

Read more from Business Insider.

Read a 2015 study in the British Medical Journal that found “cloth mask wearers had higher rates of infection than even the standard practice control group of health workers.”

Read a 2019 update to the BMJ study that reiterated the 2015 findings.

If health workers choose to work using cloth masks, we suggest that they have at least two and cycle them, so that each one can be washed and dried after daily use. Sanitizer spray or UV disinfection boxes can be used to clean them during breaks in a single day. These are pragmatic, rather than evidence-based suggestions, given the situation.

NOTE: See an interesting follow-up here.

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