Common cold and fever generally last for about three to five days. However, if it is influenza, the duration might be longer. The specific condition should be determined based on individual constitution and disease tolerance, and it generally does not exceed seven days. If the fever persists for more than a week, secondary bacterial infection or other pathogenic respiratory inflammatory factors should be considered. Chest X-rays, complete blood count, and mycoplasma tests, among other diagnostic aids, would be necessary for a precise diagnosis. Appropriate measures to reduce fever should be taken during this time.