Physical and Chemical Barriers

The human body has a range of non-specific defences that act as the first line of defence against pathogens. These defences work against all pathogens — they do not target specific ones. In this lesson you will learn about the physical and chemical barriers that prevent pathogens from entering the body.

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Overview: Lines of Defence

The body's defences can be thought of in layers:

Line of defence	Type	How it works
First line	Non-specific (physical and chemical barriers)	Prevents pathogens from entering the body
Second line	Non-specific (immune cells)	Phagocytes engulf and destroy pathogens that get past the first line
Third line	Specific (immune response)	Lymphocytes produce antibodies and antitoxins targeted at specific pathogens

This lesson focuses on the first line of defence — the physical and chemical barriers.

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Physical Barriers

1. The Skin