Nasal discharge that appears blue-green in color is primarily caused by viral infections such as the common cold, with symptoms including obvious nasal congestion, runny nose, headache, and fever. The common causative viruses include influenza virus, parainfluenza virus, and rhinovirus. We can determine the specific causative virus by testing for influenza antibodies in the blood. Based on the patient's test results, antiviral medications, as well as medicines that clear the nasal passages, are used to improve symptoms. In daily life, it is important to maintain hygiene, wash hands frequently, ensure good ventilation, wear masks, and avoid crowded places to prevent infection.