A method for blocking, neutralizing, or killing microorganisms that cause infectious disease in a mammal prior to or during the mammal encountering a contaminated environment or item includes: identifying a contaminated environment or item, wherein the contaminated environment or item is known or expected to be contaminated with harmful viral, fungal, or bacterial microorganisms； and administering a therapeutically effective amount of a barrier-forming composition to a mucosa of the mammal prior to or during the mammal encountering the contaminated environment or item. The barrier-forming composition provides a barrier on the mucosa that inhibits the microorganisms from contacting the mucosa. Other related methods are also included.
