In modern society, most diseases - whether cancer or atherosclerosis - are chronic. They are associated with genetic, psychological, social and natural risk factors. These diseases develop gradually: first symptoms appear, then a decrease in function and, finally, death occurs. Doctors usually encounter patients at the moment when the course of a chronic disease becomes dramatic - for example, chronic bronchitis turns into pneumonia or the course of atherosclerosis is complicated by the development of acute myocardial infarction. However, a doctor can help the patient at any stage - from exposure to a risk factor to the onset of an outcome, affecting the natural course of the disease.