Physical and chemical barriers prevent pathogens from getting into our body. the most comprehensive barrier is the waterproof layer of that covers the body's surface.

Picture below shows that the most comprehensive barrier is the waterproof layer of skin that covers the body’s surface. If human skin is intact, it keeps the body out of the reach of infections. The picture summarizes physical and chemical barriers against infection. 

This is the most closely resembles the model. 

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