Frank Shallenberger MD may be correct in his theory.
Another source stated that a mask will protect against droplets of saliva entering a person's body; however, a percentage of coronavirus particles are too small to be filtered by the inexpensive masks. Furthermore, these one time use masks don't provide a tight enough seal either. I try to avoid people who get too close and spit saliva when they talk, and a shield or glasses should be worn to prevent droplets from entering the mucous membranes too. An Israeli gas mask would provide better protection, but they're expensive and costly replacement filters must be changed every 12 hours.
People breathe oxygen and exhale a certain amount of carbon dioxide; therefore, wearing a mask will cause people to continually rebreathe their exhaled carbon dioxide air which is unhealthy over an extended period of time.
A mask may not be failsafe protection, but they're mandated in California. Many retail stores will not allow people to enter their facilities unless they're wearing a mask. Wearing a mask and face shield in public are probably better protection than nothing, but it's better to stay home away from people as much as possible. People who are sick should obviously quarantine themselves but that too often doesn't happen.
Unfortunately, many people out of boredom or defiance are no longer staying home and are out in public everyday possibly spreading disease, and many don't keep their distance or wear a mask. Law enforcement can't patrol specifically for mask or social distancing violations either. California Governor Newsom has mandated the closure of certain businesses, but it would have been better for the economy to allow most businesses to remain open while requiring employees and customers to wear a mask while maintaining a social distance. Many unemployed people are out in public everyday anyway, so it would be better for them to return to work under controlled conditions.
https://tbfacts.org/mask-respirator/