Entry doors of microorganisms into the human organism, bacteria, viruses. The part of the illustration on the 2/3 left explains that the bacteria and viruses are in our environment (air, water, soil, objects, food). They are also present on the surface of our body on the skin and penetrate our body through the external orifices, nose, mouth, urethra, vagina and rectum. Thus, microorganisms are found in the nasal, oral, lung, oesophage and stomach, intestinal tract, and pelvic organ exit doors. They can cross the skin barrier and penetrate the body through a wound, but also through the mucous membranes. Our body is therefore inhabited by micro-organisms. This cohabitation with some is very beneficial like the intestinal microbiota. Others are harmful and contaminate it, multiply, triggering infections. To remedy this, there are several methods of protection and struggle illustrated simply on the right side of this drawing. Prior to contamination, products may be used for preventive purposes to clean the skin (soap, hydroalcoholic gel) for aseptic (disinfection) or condom use. After contamination, a set of methods can be used to control the spread of microorganisms. This is antiseptic. After multiplication of microorganisms in the body, antibiotics can be used only to fight bacteria.