Barriers

• The skin acts as a barrier to pathogens. It also secretes antimicrobial substances which kill pathogens
• Hairs and mucus trap particles, which could contain pathogens
• The trachea and bronchi are lined with a mucus to trap pathogens
• Stomach acid kills most bacteria that enter through food
• Cilia move the trapped pathogens upwards towards the throat where they can be swallowed or coughed out