Honestly, I don’t understand how. Maybe because at least the large droplets are stopped?
But I do know there is ample evidence to indicate that they do. Dr. Rob Zatrchka said the same in one of his recent podcasts.
https://health.clevelandclinic.org/...idence-that-masks-prevent-coronavirus-spread/
Follow-up to the question as to HOW masks help: I asked a family member who had a PhD in Virology. She said that they are not perfect at prevention, but they are still effective because of 1) who they protect and 2) what they block.
When a person wears a non-surgical mask, it’s not to protect themselves, it’s to protect the people around them. Thus, it does not protect from INHALING aerosoles, if they are in the air. Rather, cloth masks help keep the moisture that carries the virus out of the air, so there is less virus in the air for others to potentially inhale.
My family member’s response was much more science-y, but hopefully I was able to provide the gist of it.
T-12 days until kickoff! Stay safe and GBR