Bacteria are tiny—so tiny that you can only see them through a microscope! They are single-celled life-forms that are both good and bad. Some forms of bacteria help with digesting food; others destroy organisms that cause disease in your body. But some bacteria cause sickness and tissue damage. Examples of harmful bacterial infections are tuberculosis, food poisoning, and pneumonia.

A virus is a non-living organism made up of genetic material (which is a fancy way of saying DNA or RNA). Viruses attack other healthy cells in your body and become mini factories, producing more viruses. Colds, the flu, warts, and the stomach “bug” are all common types of viruses.

While the name sounds fun, fungi are nothing to joke about (most of the time). A fungus cell is a eukaryote, meaning the cell contains a nucleus and other complex structures, unlike a bacteria cell. Fungi germs on the human body include athlete’s foot, mold, yeast infection, nail infections, and ringworm.