Microorganisms that are harmful to humans are pathogenic microorganisms, such as those that cause skin diseases, infectious diseases, wound infections, and food spoilage. Microorganism is a general term for tiny organisms that are invisible or not clearly visible to the naked eye. There are many types of pathogenic microorganisms, such as molds, fungi, bacteria, viruses, parasites and so on. 1. Induce skin diseases: fungi, actinomycetes and bacteria can cause deep skin tissue infections and wound infections. These harmful substances are likely to be stored on top of the skin, resulting in itching, ulceration, pain and other symptoms. 2. Causing infectious diseases: Pathogenic microorganisms can cause epidemics of infectious diseases. For example, spirochetes can cause syphilis, leptospirosis; viruses cause hepatitis, encephalitis B, measles, AIDS and other infectious diseases. Mainly through the blood transmission, is the need to give timely treatment, otherwise it will lead to aggravation of symptoms. 3. Causes infection: In addition, bacteria can cause skin disease, pus, upper respiratory tract infection, urinary tract infection, food poisoning, sepsis, and so on. Rickettsia can cause typhus and so on. Chlamydia can cause trachoma, genitourinary tract infections. Mycoplasma can cause pneumonia, urinary tract infections. 4. Make food spoilage: some microorganisms are corrosive, which can cause adverse changes in food odor and tissue structure. For example, bacteria, viruses, parasites can cause food biohazard, make food unsafe, can cause food, cloth, leather and other moldy rot. Microorganisms are closely related to human health, and careful use of antibiotics, etc., leads to dysbiosis and gives pathogenic microorganisms a chance to invade.