Experts have warned that people who have asthma or other lung conditions should not wear a face mask because it could make it difficult for them to breathe.
People have been advised to wear face masks when in public or in the midst of other people. This is because the coronavirus is a respiratory virus, meaning it infects people when it is breathed in and attaches to cells inside the airways and the lungs.
However, people who have asthma or other lung illnesses may find it difficult to breathe with face coverings.
Masks can make it more difficult to draw air into the lungs and this may trigger asthma for some patients and can also cause anxiety which changes people's breathing patterns.
The problem, however, for such people is that they are also at a higher risk of becoming seriously ill if they do catch the virus, and may be more likely to spread it when they're infectious.
Experts say people should wear a mask if they comfortably can, to protect themselves and others around them, but not risk their own health in the process.
In its official guidance, Britain's Cabinet Office now says: "If you can, wear a face covering in an enclosed space where social distancing isn’t possible and where you will come into contact with people you do not normally meet. This is most relevant for short periods indoors in crowded areas, for example, on public transport or in some shops."
But it adds: "Face coverings should not be used by children under the age of 2 or those who may find it difficult to manage them correctly. For example, primary age children unassisted, or those with respiratory conditions."
Asthma UK says: "For some people with asthma, wearing a face covering might not be easy. It could make it feel harder to breathe.
"The government has advised that people with respiratory conditions don’t need to wear face coverings, so if you are finding it hard, then don’t wear one."