The role of the immune system — a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body's own healthy tissue, according toMerck Manuals.

The immune system can be broadly sorted into categories: innate immunity and adaptive immunity.

Innate immunity is the immune system you're born with, and mainly consists of barriers on and in the body that keep foreign threats out, according to the National Library of Medicine (NLM). Components of innate immunity include skin, stomach acid, enzymes found in tears and skin oils, mucus and the cough reflex. There are also chemical components of innate immunity, including substances called interferon and interleukin-1.

Innate immunity is non-specific, meaning it doesn't protect against any specific threats.

Adaptive, or acquired, immunity targets specific threats to the body, according to the NLM. Adaptive immunity is more complex than innate immunity, according to The Biology Project at The University of Arizona. In adaptive immunity, the threat must be processed and recognized by the body, and then the immune system creates antibodies specifically designed to the threat. After the threat is neutralized, the adaptive immune system "remembers" it, which makes future responses to the same germ more efficient.