Good Morning Britain 's Dr Sarah Jarvis has warned against removing your mask in a restaurant and then putting it back on when you leave.
She said you must put a clean one back on, and also warned not to pull it down over your chin and then back up over your mouth and nose.
This is because you can contaminate your mask with your hands, or even your chin and neck, then place it back over your mouth and infect yourself.
She was reacting to a baffling video from the US where restaurant diners were wearing two masks, one over each half of their mouth, opening their mouths to let in the food and completely defeating the point.
The debate came as new face covering rules were recently placed in in England, making them compulsory in shops, supermarkets and some takeaways depending on the nature of your visit.
Speaking about eating while wearing a mask effectively, she said: "Clearly that is not feasible when you’re eating, so you take your mask off. Ideally, you take it off from behind.
"Do not touch your face and please do not just put it back on again when you leave the restaurant because the problem with that is you could contaminate your hands and your mask might have virus on it."
She added that this means taking one spare mask with you out in public so you can easily swap it for your dirty one.
Dr Sarah also debunked claims anti-malaria medication hydroxychloroquine that was promoted by Donald Trump's son, treated coronavirus effectively.
Trump has now endorsed using the medication to treat coronavirus, and the show played a clip of him claiming people only want to say it does not treat coronavirus because he recommended it and people do not like him.
Sarah said this if definitely not the case, and explained that the medication was generally used for lupus and could affect the heart.
This means it would be particularly risky to give it to patients with coronavirus because there is already a risk to the heart.
* Good Morning Britain airs on weekdays on ITV at 6am
