So as an EHS specialist in will add the following:
Mask - depends on the income but yes there are mask that do seal 100% to your face when don correctly. However, a medical evaluation is required in the business sector prior to use per OSHA (there are cases where people fail the evaluation and are NOT permitted to wear them for health reasons). Mask do have a life span, cloth face coverings are not "mask" defined by OSHA.
The fibers you can breath in from disposable paper mask (wearing past life span or incorrectly) could be harmful (need more research).
In certain industries and environments mask can cause a hazard (heat, welding, electric, food, machining) if the wrong kind is used.
In general public areas where no other physical hazards are present: face coverings can help prevent spit from landing in your mouth from others. Try spotting into someone's mouth when you are wearing a mask.
This is the and of my .02