Summary:
- The body’s first line of defense consists of different types of barriers that keep most pathogens out of the body.
- Pathogens are disease-causing agents, such as bacteria and viruses.
- The skin is the most important mechanical barrier.
- Chemical barriers destroy pathogens on the outer body surface, at body openings, and on inner body linings.
- Sweat, mucus, tears, and saliva all contain enzymes that kill pathogens.
- Urine is too acidic for many pathogens, and semen contains zinc, which most pathogens cannot tolerate.