Every Monday, we’ll answer your questions on Covid-19 and health in a feature published online. You can submit a question here.

This week, HuffPost UK reader Jill asked: “Could licking envelopes before posting Christmas cards spread the virus?”

We all know by now that the virus behind Covid-19 can live on surfaces for up to 72 hours (or three whole days). A well-cited study found SARS-CoV-2 can survive for up to 24 hours on cardboard and up to three days on plastic and stainless steel.

This means that, hypothetically, the virus could be lurking on your Christmas card envelopes. However, there are some important things to remember before you dust off the hazmat suit prior to opening your post.

While the virus can last on surfaces for a long time, it doesn’t necessarily mean that there would be enough viable virus on your Christmas card envelope to infect you or postal workers. A study conducted early on in the pandemic found the virus lost infectivity on paper within three hours, says Professor Mark Harris, from the School of Molecular and Cellular Biology at the University of Leeds.

The average Christmas card envelope will probably have spent more than three hours sitting in a postbox alone, waiting to be collected. By the time it’s been through the postal service, three hours will most definitely have passed.

Prof Harris tells HuffPost UK it is “highly unlikely” you’d spread Covid by licking an envelope – or catch it by touching an envelope that had been licked. Phew. 

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It’s widely agreed the main way the virus spreads is through person-to-person contact. “Inanimate surfaces play a very small part in transmission of Covid. The vast majority of cases are person-to-person, spread through respiratory droplets,” Dr John Segreti, medical director of infection control and prevention at Rush University Medical Centre in the US, told The Chicago Tribune. 

And on the risk of sending and receiving Christmas cards, Dr Segreti added: “If there is any risk at all, it’s got to be incredibly low.”

Professor Sally Bloomfield, honorary professor at the London School of Hygiene and Tropical Medicine and chair of the International Scientific Forum on Home Hygiene, agrees the risk is very small. But it’s also not zero, she points out.

“The risks from ‘surfaces’ are mainly associated with surfaces frequently and recently touched by other people who, if they happen to be infectious, may have virus on their hand,” she says. “This is why over Christmas it is important to avoid touching these surfaces as much as possible.”

The Christmas cards you receive in the post will probably have been handled by a few different people to get to you safely, so you’re best off washing your hands after opening your mail – regardless of whether it’s been sealed with a lick or not. Royal Mail workers are also urged to maintain good hand hygiene to keep themselves safe.

“If people are worried, leave the post in your letter box or on the doormat for three hours before opening it,” suggests Professor Harris. “If you want to open it immediately ensure you wash your hands afterwards.”