Flexi Says: (1) Mechanical barriers physically block pathogens from entering the body. The skin is the most important mechanical barrier. (2) Chemical barriers destroy pathogens on the outer body surface, at body openings, and on inner body linings. Sweat, mucus, tears, and saliva are all chemical barriers. They all contain enzymes that kill pathogens. (3) Biological barriers are living organisms that help protect the body. Millions of harmless bacteria live on the human skin and in the GI tract
