Question: Select examples of chemical barriers to infection in the human body. The low pH in the stomach kills pathogens entering the digestive system. Enzymes in saliva break down pathogens entering the mouth. Antibodies recognize pathogens and attack infected cells. Hairs located in the ears and nose block pathogens. Cilia in the respiratory system move pathogens trapped in mucus to the mouth. Macrophages phagocytize pathogens in the body. Need Assignment Help?