Face masks become much less effective in protecting from, or minimizing the spread of, the coronavirus when they are wet, according to the World Health Organization (WHO).

Guidance on wearing face masks in public spaces is becoming more widespread across Europe, with masks even becoming mandatory outdoors in Italy and some regions of Spain.

But as the fall season creeps up on parts of the continent, the possibility of increasingly wet weather is bringing its own set of problems to the correct use and effectiveness of face masks.

Scientists warn that wet face masks should be replaced immediately, as water restricts the airflow, affecting the mask's ability to filter viral particles.

The WHO's guidance is that "all masks should be changed if wet or visibly soiled – 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."

Guidance on removing masks should also be followed when discarding a damp face mask to avoid self-contamination.

"Remove the mask without touching the front of the mask, do not touch the eyes or mouth after mask removal. Either discard the mask or place it in a sealable bag where it is kept until it can be washed and cleaned. Perform hand hygiene immediately afterwards."

Official guidance from the UK's Department of Health and Social Care also explains that the public should "change the face covering if it becomes damp or if you’ve touched it."

But experts are calling on more public health campaigns to ensure people understand the potential risks of wearing wet face masks and what to do to eliminate the risk. 

Carrying a spare face mask may be a handy way of making sure you can swap a wet face mask if you've been caught in the rain.