A bad cough after a cold may be caused by untreated or incomplete treatment of the cold resulting in bacterial or viral involvement of the bronchi, causing pharyngitis, bronchitis, or pneumonia; it may also be a persistent cough caused by mycoplasma or Mycobacterium tuberculosis infection. Coughing can occur when there are excessive airway inflammatory secretions that irritate the airways. If you have a cough with sputum and sore throat after a cold, consider chronic bronchitis caused by an uncontrolled bacterial infection, and take sputum culture to clarify the pathogenic bacteria. If the cough is dry, it may be mycoplasma infection, and azithromycin can be given for one week to observe the efficacy of the treatment, and sputum culture is also feasible to clarify the presence of mycoplasma infection. Empirical anti-tuberculosis treatment is also feasible after blood collection, and if the symptoms are reduced after taking anti-tuberculosis drugs, it can further support Mycobacterium tuberculosis infection. It can be seen that coughing after a cold is often due to the presence of pathogenic bacteria infection. Therefore, if you have a cough that persists, you should consult a regular hospital’s inhalation department and cooperate with your doctor to perform relevant tests to identify the cause and treat it promptly.