According to the Textbook of Bacteriology, the body's first line of defense against infection is known as innate immunity. Innate immunity consists of the body's specific natural defenses against infection.
The Textbook of Bacteriology states that the human body's first line of defense consists of the skin and the mucous membranes. These tissues block infection by using both physical and chemical barriers. If infectious organisms get past the skin and the mucous membranes, the body activates cells that attempt to destroy the invaders. The strength of innate immunity depends on various factors including genetics, diet, age, sex, medications, illness and injury.