Who should wear a face mask, and do they stop the coronavirus?

• Masks work by capturing droplets that are dispersed in coughs, sneezes and breath - these are the main transmission route of the new coronavirus.
• Some masks have a valve in the front to help prevent moisture in exhaled breath condensing on the inside, making the mask wet and more liable to virus penetration.

* The World Health Organization's advice is that if you are healthy, you only need to wear a mask if:

- you are caring for someone with suspected or confirmed COVID-19 infection

- you are coughing or sneezing yourself, or suspect you might have COVID-19.

* Masks work by capturing droplets that are dispersed in coughs, sneezes and breath - these are the main transmission route of the new coronavirus.

* There are two main types of mask: surgical masks, which are strips of fabric worn across the nose and mouth and closer-fitting ones sometimes called respirators.

* Close-fitting masks - such as ones - can offer good, but not total protection against infectious droplets, while the next rank up - the N99-rated masks - can give better protection, but some find them difficult to breathe through.

* The "N" rating relates to the percentage of particles of at least 0.3 microns in diameter that the mask is designed to block: N95 masks stop 95% and N99 masks stop 99%.

* Some masks have a valve in the front to help prevent moisture in exhaled breath condensing on the inside, making the mask wet and more liable to virus penetration.

* Masks are only effective if you combine wearing them with frequent hand washing and ensure you don't touch your face.

* Anyone using a mask should make sure their hands are thoroughly cleaned with soap and water or an alcohol-based hand sanitizer before putting it on.

* The mask should cover your mouth and nose, and there should be no gaps between your face and the mask.

* As much as possible, avoid touching the mask.

* When the mask becomes damp, replace it with a new one. Do not re-use single-use masks.

"Wearing a mask can also reduce the propensity for people to touch their faces, which happens many more times a day than we all realise and is a major source of infection without proper hand hygiene," said Stephen Griffin, an associate professor at Leeds University's Institute of Medical Research.