The common cold generally follows a process. Eighty percent of common colds start as viral colds, characterized by nasal congestion, runny nose, sneezing, and other catarrhal symptoms. Generally, after three to five days, these catarrhal symptoms gradually disappear, as the virus is self-limiting. If the symptoms do not improve after three to five days and are accompanied by coughing, purulent sputum, and fever, it may have progressed to a bacterial cold, which requires antibiotic treatment. When we commonly refer to a persistent cold, we mainly refer to a cough. Some people might experience a cold for more than ten days, or repeatedly suffer from a dry cough. At this time, it's not that their cold hasn't healed; rather, it's because the respiratory tract has been damaged and needs time to recover. Typically, this kind of irritating dry cough without sputum generally lasts for a while.