People who wear face masks could be putting themselves more at risk of contracting coronavirus, England's deputy chief medical officer has warned.
Dr Jenny Harries said it is "not a good idea" for the average member of the public to put on a face mask unless they have been advised to by a healthcare worker.
Speaking to BBC News on Thursday, she warned the virus could even become trapped in face masks, resulting in the wearer breathing it in.
Dr Harries said: "For the average member of the public walking down a street, it is not a good idea.
"What tends to happen is people will have one mask. They won't wear it all the time, they will take it off when they get home, they will put it down on a surface they haven't cleaned.
"Or they will be out and they haven't washed their hands, they will have a cup of coffee somewhere, they half hook it off, they wipe something over it.
"In fact, you can actually trap the virus in the mask and start breathing it in."
Asked if people are putting themselves more at risk by wearing masks, Dr Harries said: "Because of these behavioural issues, people can adversely put themselves at more risk than less."
Dr Harries said people should wear masks when they are advised to by healthcare workers, particularly if they have tested positive for Covid-19, as it can "prevent any virus from coming out".
The World Health Organisation (WHO) said healthy individuals only need to wear a mask if they are taking care of a person with a suspected coronavirus infection.
WHO said masks are only effective when used in combination with frequent hand washing, and must be disposed of properly.