A cold can cause a yellow runny nose. Cold is a generic term for upper respiratory tract infection, which is mainly caused by inflammation of the mucous membrane of the upper respiratory tract due to a decrease in the body’s resistance to invasion by pathogens. 80% of cold is caused by viral infections, which usually results in nasal congestion, runny nose, sneezing, clear nasal discharge, coughing up sputum, and coughing up clear sputum. A small percentage of colds are initially caused by bacterial infections, which may result in a yellow pus nose and yellow pus sputum. In addition, some of the colds caused by viral infections secondary to bacterial infections may also have a yellow runny nose. Generally, anti-bacterial treatment with sensitive antibiotics, such as penicillin, amoxicillin, clindamycin, etc., is required.