Microbes are microscopic organisms that live on and inside humans. There are around 100 trillion microbes on the average person. Microbes can be classified as pathogenic ("bad") or non-pathogenic ("good"). Pathogenic microbes include bacteria, fungi, viruses, protozoa, and helminths, which make up approximately 3% of microorganisms and can cause diseases and infections in humans. The document then provides examples of diseases and infections caused by different pathogenic microbes.