What is an infection? Infection is a process in which disease-causing microorganisms invade the body, multiply in the body, cause various degrees of damage to the body, and then gradually resolve under the action of the body’s immunity or medication. If the pathogenic microorganism’s ability to cause disease and multiply exceeds the body’s immunity and the inhibitory effect of drugs, it will lead to progressive aggravation of the infection and eventually cause the patient’s death. Regardless of the consequences, the body will experience redness, swelling, heat, pain, and other uncomfortable symptoms and even reduced function during the struggle between the disease-causing microorganisms and immunity/drugs, and this type of infection is called “overt infection”. In contrast, “latent infections” are called “hidden infections” in which the pathogenic microorganisms are less capable of causing disease, reproduce more slowly, or the body’s resistance is too strong, resulting in the onset, development, and end of the infection very insidiously, and the patient has almost no symptoms. This type of infection can also stimulate the body’s immune system to produce antibodies against the disease-causing microorganism, sometimes with some minor signs of organismal destruction (e.g., fibrous streaks of latent tuberculosis infection). In a sense, occult infections are not only largely harmless, but even beneficial, because they stimulate the body’s immune system to produce specific immunity (antibodies) against a disease-causing microorganism, which can sometimes last a lifetime (e.g., measles and smallpox), and vaccines are prepared using this principle. It is clear that the immunity of the organism is not only related to innate conditions, but can also be developed later in life. One more thing, although the body’s resistance is important in maintaining human health, the onset of many diseases is not related to infection (for example, many cardiovascular and endocrine diseases), and the maintenance of health requires efforts in many areas.