Dr Hilary Jones has issued a stark warning on how long you can actually wear a face mask for before it becomes useless.
Appearing on today's episode of Good Morning Britain, the medical expert told viewers how quickly face coverings can turn futile.
According to the latest government rules and regulations, face coverings need to be worn as a legal requirement in retail and hospitality venues.
However, the 67-year-old spoke out about a study that found people were failing to wear their face masks or face coverings correctly and know when to replace one with a new one.
Speaking to hosts Charlotte Hawkins and Kate Garraway, Dr Hilary warned: "It has always been the case that one of the criticisms of mask wearing was people not wearing them correctly.
"And actually you almost need a degree in microbiology to wear a face mask correctly.
"It has to be sterile to begin with and it needs to be kept sterile."
He went on to discuss the correct usage of face masks, adding: "You should not touch it because this could contaminate it.
"If you wear a disposable mask, keep it for three hours, chuck it away and wear the next one.
"Be careful when you are putting it on - wash your hands etc.
"If you are using a reusable one, wash it on 60 degrees with an ordinary washing powder."
Good Morning Britain continues to air each weekday from 6am on ITV1.
It will return next Monday with Piers Morgan and Susanna Reid back in the studio.
