There are many reasons for dry cough after cold, such as mycoplasma pneumonia, allergic cough, tuberculosis, tumors and so on. 1. Mycoplasma pneumonia: patients may have lowered immunity after catching a cold, secondary to Mycoplasma pneumonia, manifested as persistent dry cough, chest pain, initial weakness, generalized body aches and pains. 2. Allergic cough: patients may have allergic cough secondary to cold, manifested as paroxysmal, irritating cough, daytime and nighttime cough, some patients have a foreign body sensation in the throat and itchy, belonging to chronic cough. 3. Tuberculosis: patients may have tuberculosis secondary to colds, manifesting as dry cough, fatigue, night sweats, weight loss, low fever, etc. 4. Tumor: It is also possible that the patient has lung tumor or pleural tumor, which is secondary to lung infection, causing cold symptoms, such as cough, sputum, fever, etc., because the tumor stimulates the mucous membrane of the airway, causing irritating and persistent cough. After the cold has been dry cough may also have other causes, such as post-infectious cough airway hyperreactivity, cough variant asthma, etc., in addition to gastroesophageal reflux stimulation and upper airway cough syndrome can not be ignored, the patient should be timely medical attention to clarify the cause of the disease, early treatment, so as not to delay the condition.