Yellow phlegm in the throat in the morning is, first of all, a sign of inflammation in the throat, caused by bacterial infection. The inflammatory area will be congested and edematous, and there will also be exudation, sometimes with a bloody or inflammatory substance. In addition, neutrophils or phagocytes in the body may gather in the throat to swallow bacteria, and then lysis and necrosis may occur. These lysed and necrotic bacteria and inflammatory substances are mixed together to form yellow sputum. During the daytime, there is a lot of swallowing and food swallowing, and this yellow phlegm may enter the digestive tract with swallowing. However, at night, these inflammatory substances as well as necrotic substances of phagocytes remain in the throat, so that coughing yellow sputum occurs in the morning and antibiotics are needed for treatment.