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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