Hello Dear There are lot of causes for persistent cough. Allergic reaction is the most common one. You need to visit a physician or pulmonary specialist who may do a blood test to see allergic content that is eosinophilia. Other causes for persistent cough may be infective conditions like Tuberculosis. A detailed test including Xray, Spirometry etc is required. But you say that its all done and shows normal report. In that case it might be definitely due to allergy. So you need to try to find out which is the source of your allergen. It may be due to pollen, dust, some particlular food like fish or meat, or cat hair etc Hope I have answered your question. Feel free to contact me if you have any more questions. I ll be glad to help you. All the best With warm regards Dr Sanjay Kini