The possible reasons for a long term bad cold are: low resistance of the body, incomplete treatment or new infection, and disease factors. 1. Low body resistance: In case of excessive fatigue or stress, or suffering from diseases affecting immunity, such as AIDS, etc., the body’s immune function is low, which cannot resist the invasion of pathogens well, and it is easy to be infected and not easy to get well. 2. Incomplete treatment or new infections: When the treatment is incomplete, the pathogens are not completely eliminated or other pathogens are infected, thus causing the cold to be bad for a long time. 3. Disease factors: If you suffer from leukemia, lymphoma, etc., the clinical manifestations can be similar to the symptoms of colds, which can be mistaken for colds. If the cold does not get better for a long time, you need to pay attention to it, and it is recommended to go to the hospital in time and find out the cause, according to the cause of the disease under the guidance of the doctor to carry out the right treatment.