Evidence-based
Immunity & Infectious Disease
Written by:
Fact-checked by:
•Last Updated: August 16, 2022
Infectious diseases are caused by microbes, which broadly fall into four categories: bacteria, viruses, fungi, and parasites. Microbes are present in the environment, as well as in and on the human body. The immune system is our body’s defense system against microbes. It differentiates “self” from “nonself” and mounts a response to anything that is foreign to the body.
