Face masks are less effective in the rain at stopping the spread of coronavirus, health experts and scientists have warned.
The UK government and the World Health Organization (WHO) have both instructed users to replace their masks if they get wet.
The effect of wet weather on the spread of COVID-19 has become a key issue after heavy rainfall across Britain in the past week.
On Tuesday, Tim Spector, professor of genetic epidemiology at King’s College London, told The Times that the public should be given new advice on wearing face masks in the rain.
Watch: How to remove a face mask correctly
Prof Spector, who is leading the COVID Symptom Study app, told the newspaper: “It would now be useful if clear advice were issued to the public.
“Masks need to be changed regularly and this is particularly important to understand in damp and wet weather.”
Prof Spector previously revealed that thousands of people in the UK are suffering from so-called “long COVID”, where coronavirus symptoms persist for longer than a month.
In their respective guidelines, both the WHO and the Department of Health and Social Care currently advise people to replace their masks if they become damp.
While masks are not mandatory in the UK while outside, many people choose to keep them on even when they are not indoors.
Dr Aseem Malhotra, a consultant cardiologist, told The Times: “It is obvious that masks will get damp as people shop and travel in bad weather.
“There has been no public campaign to make people aware that this can make their masks ineffective.”
In its guidance on face coverings, the UK government says users should “change the face covering if it becomes damp or if you’ve touched it”.
The WHO advises people to “replace masks as soon as they become damp with a new clean, dry mask”.
It also warns of the “potential self-contamination that can occur if medical masks are not changed when wet, soiled or damaged”.
When a face mask is wet, the moisture can result in an increased resistance to airflow.
Professor Karol Sikora, a former head of the WHO cancer programme, also told The Times: “Moisture makes masks porous and because of this all types of mask are essentially vulnerable in damp weather.”
Watch: Why are UK deaths so low as cases rise?
Coronavirus: what happened today
Click here to sign up to the latest news and information with our daily Catch-up newsletter