The change from yellow sputum to white sputum for a cold is mainly due to induced factors such as cold, rain, and immune decline of the body, which causes the body to be infected by pathogens such as bacteria, resulting in congestion, edema, and exudation of a large amount of inflammatory substances from the mucous membrane of the upper respiratory tract, resulting in the discharge of yellow-purulent-colored secretions. With the improvement of the immune system and the intervention of anti-bacterial therapy, the bacteria slowly decrease, the cold improves, and the sputum becomes white. In other special cases, although the bacteria that caused the cold are eliminated, there may be other pathogenic infections, such as mycoplasma and chlamydia, etc. Blood tests can be performed, and if necessary, sputum can be taken for culture of pathogens to clarify the diagnosis and provide symptomatic and etiological treatment.