Scientists have warned that a wet face mask is less effective because water restricts airflow and cuts the amount of viral filtering.
The World Health Organization says dry three-layer mask worn over the mouth and nose can protect people from catching the coronavirus.
However, a former senior WHO official urged the public to change their face covering if it gets wet because moisture makes masks "porous."
Keeping face masks dry
Professor Tim Spector warned the Government that the public is not aware of the risks involved with a wet face mask. He said that it would be useful if clear advice were issued to the public.
The warning comes as the UK is about to enter the autumn season, with rain showers and storms expected. The Met Office has forecast more rainy days and periods of prolonged rainfall.
A former official in the WHO's cancer program, Karol Sikora, told The Times that moisture makes masks porous and because of this, all types of masks are essentially vulnerable in damp weather.
Dr. Simon Clarke, an associate professor of Cellular Microbiology at the University of Reading, told MailOnline that a damp mask is no different from a dirty handkerchief tied to the face.
Dr. Clarke said that if the mask becomes damp from the water vapor in the breath or through sneezing and coughing, this is a good sign that you need to put a new or cleanly laundered replacement mask on anyway.
Clarke added that the advice on wearing face coverings mentions that those made of cloth should be constructed of a material that is as densely woven as possible to prevent any droplets from escaping while still allowing you to breathe.
Also, depending on how wet the material is, there could be an impact on the size of the holes in the fabric, either it makes them too large to prevent droplets getting in or out, or it makes them too narrow to allow you to breathe properly.
Dr. Clarke said that he always makes sure that he has at least one spare, clean facemask with him whenever he goes out so that he can replace the one that he is wearing if it gets wet or if he has been wearing it for a while, and he encourages everyone to do the same.
Resistance to airflow
According to The Nursing Times, wet face masks suffer from increased resistance to airflow, and are therefore less efficient at filtering bacteria and has increased venting. Venting is when more air and droplets are expelled by the mask.
The WHO backed up this warning from medical experts and stated online that all masks should be changed if it is wet or if it is visibly soiled.
According to WHO, a wet mask should not be worn for an extended period of time. Replace masks as soon as they become damp with a new clean, dry mask. Other experts also called for the Government to warn the public about the dangers of using wet and soiled face masks.