Does it matter what sort of mask you wear?

Yes. Different types of mask offer different levels of protection. Surgical grade N95 respirators offer the highest level of protection, preventing the user from becoming infected with Covid-19, followed by surgical grade masks. However, these masks are costly, in limited supply, contribute to landfill waste and are uncomfortable to wear for long periods. So even countries that have required the public to wear face masks have generally suggested such masks should be reserved for health workers or those at particularly high risk.

The evidence on the protective value of single-use paper masks or reusable cloth coverings is less clear, but still suggests that face masks can contribute to reducing transmission of Covid-19. Analysis this week by the Royal Society said this included homemade cloth face masks.

The evidence on any mask use, outside of surgical masks, is still emerging: there appears to be some benefit, but the exact parameters of which masks are the best and the extent to which they protect the wearer or those around them are still being figured out. A tighter fitting around the face is probably better, but the CDC suggests any covering, including a bandana, is better than none.

R, or the 'effective reproduction number', is a way of rating a diseases ability to spread. Its the average number of people on to whom one infected person will pass the virus. For an R of anything above 1, an epidemic will grow exponentially. Anything below 1 and an outbreak will fizzle out eventually.

At the start of the coronavirus pandemic, the estimated R for coronavirus was between 2 and 3 higher than the value for seasonal flu, but lower than for measles. That means each person would pass it on to between two and three people on average, before either recovering or dying, and each of those people would pass it on to a further two to three others, causing the total number of cases to snowball over time.

The reproduction number is not fixed, though. It depends on the biology of the virus; people's behaviour, such as social distancing;and a populations immunity.

Hannah DevlinScience correspondent

One US study investigated which household materials best removed particles of 0.3-1.0 microns in diameter, the typical size of viruses and bacteria, and concluded that good options include vacuum cleaner bags, heavyweight quilters cotton or multiple layers of material. Scarves and bandana material were less effective, but still captured a fraction of particles.

Before putting on a mask, clean your hands well with soap and water. Cover the mouth and nose with your mask and make sure there are no gaps between your face and the mask. Avoid touching the mask while using it and, if you do, wash your hands. Replace the mask when it is damp. To remove your mask, take it off using the elastic tags, without touching the front and discard immediately into a closed bin or, if the mask is reusable, directly into the washing machine.

They should be washed after each use. The US Center for Disease Control suggests routinely.

Many commercially available masks are made from layers of plastics and are designed to be single-use. According to an analysis by scientists at University College London, if every person in the UK used one single-use mask each day for a year, an extra 66,000 tonnes of contaminated plastic waste would be created. The use of reusable masks by the general population would significantly reduce plastic waste and the climate change impact of any policy requirements for the wearing of face masks, according to the UCL team, led by Prof Mark Miodownik. They say that according to the best evidence, reusable masks perform most of the tasks of single-use masks without the associated waste stream.

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What kind of face mask will best protect you against coronavirus? - The Guardian