Table 1.

The four barriers of innate immunity

Physical barriers	Skin	Skin epidermis prevents pathogen invasion Skin pH maintained between 3 and 5 by sebum to inhibit growth of pathogens
	Mucosal membrane	Mucosal membrane traps pathogens
Physiological barriers	Temperature	Temperature affects survival of invading pathogens
	pH	Acidic environment of stomach kills pathogens
	Chemical mediators	Lyse cell walls of invading pathogens
Phagocytosis	Neutrophils, macrophages, dendritic cells
Inflammation	Clearing invading pathogens via complex events