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 against Covid-19 infection, 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 by the Royal Society said this included homemade cloth face masks. Are paper surgical single-use masks better or is a cloth mask OK? 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. 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 “quilter’s cotton” or multiple layers of material. Scarves and bandana material were less effective, but still captured a fraction of particles. How do you take them on and off safely? 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. How often do you need to wash masks? They should be washed after each use. The US Center for Disease Control suggests “routinely”. Is there an environmental concern? 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. • This article was amended on 12 May 2020 to clarify that N95 masks alone do not guarantee protection from Covid-19 infection. • This article was further amended on 5 June 2020 to take in new guidance issued by the World Health Organization • Due to the unprecedented and ongoing nature of the coronavirus outbreak, this article is being regularly updated to ensure that it reflects the current situation as best as possible. Any significant corrections made to this or previous versions of the article will continue to be footnoted in line with Guardian editorial policy.