Editing Immunology (section)

=== Physical and Chemical Barriers ===
Before cellular mechanisms are even required, a pathogen must bypass strict anatomical barriers. The skin provides a tough, impermeable physical barrier, while mucosal membranes in the respiratory and digestive tracts trap microbes. Chemical barriers, such as the highly acidic environment of the stomach and antimicrobial enzymes (like lysozyme in tears and saliva), actively destroy incoming pathogens.