List three physical and chemical barriers that pathogens encounter when they try to enter the human body?

Pathogens encounter several physical barriers when trying to enter the human body, including the skin, which acts as a protective barrier, and mucous membranes that trap pathogens in respiratory and gastrointestinal tracts. Chemical barriers include antimicrobial peptides found in skin secretions and enzymes like lysozyme in saliva and tears that break down bacterial cell walls. Additionally, stomach acid creates a harsh environment that can kill many ingested pathogens. Together, these barriers form the first line of defense against infections.