Okay, George. I looked up propylene glycol and found that is a compound used to make antifreeze and de-icing solutions for cars, airplanes, and boats; to make polyester compounds; and as solvents in the paint and plastics industries.*
That being said, I also learned you are absolutely correct; it is basically harmless. Thank you for setting me straight!!
So I'm going to go out and buy some Tucks and start using them as part of a grand experiment (and also because I'm lazy and using wipes will be easier than washing with Neutrogena and water). The only downside to this experiment is since I'm doing this to see if Tucks decreases the lifetime of the mask by causing undue degradation of the material, it will take several weeks/months to determine. But I will stay the course and report my findings!
*Source: ATSDR (AGENCY FOR TOXIC SUBSTANCES AND DISEASE REGISTRY)ToxFAQs™for Ethylene Glycol and Propylene Glycol