This study is an exploratory clinical trial. It is intended to investigate the efficacy of mesenchymal stem cell-derived exosome nebulization in the treatment of postinfectious cough through a randomized controlled clinical study, with a view to providing better treatment options for patients with postinfectious cough, improving their quality of life, and providing reference data for the subsequent multi-center clinical trials.

Inclusion Criteria:

1. Patients aged 18-60 years.
2. Diagnosis of post-infectious cough, which is defined as: after the symptoms of acute respiratory infection have disappeared, chest radiographs are normal, irritating dry cough or cough with small amounts of mucoid phlegm occurs, cough persists for 3 to 8 weeks, and other causes of cough are ruled out.
3. Baseline cough visual analog scale>=60mm.

Exclusion Criteria:

1. patients with any other disease that causes coughing (eg, Upper airway cough syndrome, eosinophilic bronchitis, gastroesophageal reflux cough, bronchial asthma, chronic obstructive pulmonary disease and bronchiectasis).
2. Patients with serious lung diseases (eg, lung cancer, tuberculosis or pulmonary fibrosis).
3. Patients with serious comorbidities, (eg, cardiovascular, cerebrovascular, liver, kidney or hematopoietic system diseases or other serious primary diseases)
4. Current or ex-smokers quitting smoking for less than 6 months.
5. Patients with a body temperature ≥37.3℃.
6. Patients with white blood cell count or neutrophil count is higher than the upper limit of normal.
7. Patients with abnormal chest X-rays.
8. Patients Suspected or confirmed history of alcohol or drug abuse or mental illness.
9. Patients with pregnancy, lactation or planning pregnancy.

All shared IPD will be de-identified to protect participant privacy, with direct identifiers (e.g., name, contact information, medical record numbers) removed or anonymized. Access to the data will be restricted to authorized researchers with a valid research proposal, ensuring the data is used only for purposes consistent with the original study's goals (e.g., secondary analyses of treatment efficacy or safety).