Jenny Harries, deputy chief medical officer, said the masks could “actually trap the virus” and cause the person wearing it to breathe it in.
“For the average member of the public walking down a street, it is not a good idea” to wear a face mask in the hope of preventing infection, she added.
Sales of the masks have sky-rocketed since the Covid-19 outbreak began, with retailers including Boots and Amazon selling out of the products before the virus had even taken hold in the UK.
Asked about their effectiveness, Dr Harries told BBC News: “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 added: “Because of these behavioural issues, people can adversely put themselves at more risk than less.”
However, she said those who are advised to wear one by healthcare workers should follow their guidance.
Demand for face masks in China, where the coronavirus outbreak began, exceeded 200 million a day in January, prompting manufacturers to cancel staff leave and increase wages to ramp up production.
But Jake Dunning, head of emerging infections and zoonoses [infectious disease spread between humans and animals] at Public Health England, told The Independent there was “very little evidence of a widespread benefit” from wearing them.
“Face masks must be worn correctly, changed frequently, removed properly, disposed of safely and used in combination with good universal hygiene behaviour in order for them to be effective,” he added.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies