STIs are caused by microorganisms that enter the body of a healthy person along with blood, semen and vaginal secretions, and some diseases, such as herpes or genital warts, are spread by direct contact with infected skin. Currently, there are 31 pathogens for which sexual transmission is possible: 15 types of bacteria, 10 different viruses, 3 types of protozoa, 2 types of ectoparasites and 1 type of fungi. As you can see, there are quite a few pathogens, and each of them individually can cause irreparable harm to health. The insidiousness of these infections (especially viral ones) is that there are often no pronounced symptoms that could indicate the onset of the disease.