Wearing two masks could improve protection from Covid-19 by up to 90% - according to a new study

The CDC recommends doubling up on masks (Photo: Jeff J Mitchell/Getty Images)

Research from the US Centres for Disease Control and Prevention (CDC) has found that people can increase their protection from virus droplets by 90 per cent by “double masking”.

The study says: “Based on experiments that measured the filtration efficiencies of various cloth masks and a medical procedure mask, it was estimated that the better fit achieved by combining these two mask types, specifically a cloth mask over a medical procedure mask, could reduce a wearer’s exposure by >90 per cent.”

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The US’s top infectious disease expert, Dr Anthony Fauci, has recommended the practise of double masking in the past, however this is the first CDC backed research to also advise doubling up on masks.

Double masking ‘blocks 92.5% of cough particles’

The study also found that an unknotted medical procedure mask alone blocked only 42 per cent of particles from a simulated cough, and a cloth mask alone blocked 44.3 per cent.

However, the combination of the cloth mask covering the medical procedure mask blocked 92.5 per cent of cough particles.

Speaking in a briefing from the White House Covid-19 Response Team, CDC Director Rochelle Walensky said: “In the study, wearing any type of mask performed significantly better than not wearing a mask.

“And well fitting masks provided the greatest performance at both blocking emitted aerosols and exposure of aerosols to the receiver. In the breathing experiment, having both the source and receiver wear masks modified to fit better reduced the receiver’s exposure by more than 95 per cent compared to no mask at all.”

The study says: “Universal masking is a highly effective means to slow the spread of Sars-CoV-2 when combined with other protective measures, such as physical distancing, avoiding crowds and poorly ventilated indoor spaces, and good hand hygiene.”

Double masking shouldn’t be applied to all masks however - for example, you should not double mask using two disposable masks.

The CDC says: “Disposable masks are not designed to fit tightly and wearing more than one will not improve the fit.”

Modifying masks to fit better

As well as looking into the use of double masking, the CDC also conducted research into ways to make masks fit better, and the effect that these changes has on providing extra protection.

The CDC found that “knotting the ear loops of a medical procedure mask and then tucking in and flattening the extra material close to the face” substantially “improved source control and reduced wearer exposure”.

“These experiments highlight the importance of a good fit to maximise mask performance,” the CDC states.

The study found that in lab tests with dummies, exposure to potentially infectious aerosols decreased “by about 95 per cent” when both dummies wore tightly fitted masks.

CDC guidance on choosing a mask

The CDC says:

  • You should choose a mask with a nose wire, as this prevents air from leaking out the top of the mask
  • You should make sure that the mask fits snugly over your nose, mouth and chin
  • You should add layers of material to the mask, either by using a cloth mask with multiple layers of fabric, or by wearing a disposable mask under a cloth mask