After taking antibiotics, all bacteria, whether beneficial or harmless, will be eliminated. Therefore, the antibiotics used now are generally broad-spectrum antibiotics. Compared with narrow-spectrum antibiotics, the scope of application of lethality is also wider. For example, in order to protect the intestinal flora of human body, bacteria must be used for protection. If the bacteria are killed, it will cause great damage to the bacterial composition in the digestive tract, resulting in allergies, eczema, constipation and other diseases.