Innate immunity is the body’s first line of defense against pathogens and other harmful substances. It is essentially made up of barriers that aim to keep viruses, bacteria, parasites, and other foreign particles out of your body or limit their ability to spread and move throughout the body. The innate immune system includes physical barriers such as skin, the gastrointestinal tract, the respiratory tract, and the urinary tract. It also includes chemical barriers such as enzymes in tears and skin oils that kill bacteria. The innate immune system relies on the recognition of particular types of molecules that are common to many pathogens but are absent in the host. These pathogen-associated molecules stimulate two types of innate immune responses—inflammatory responses and phagocytosis by cells such as neutrophils and macrophages.
