You do need to be concerned about the development of a cough that has lasted for 3 months, making it chronic. It could be due to your 15 years of
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Smoking - tips on how to quit
Smoking and copd (chronic obstructive pulmonary disorder)
Smoking and smokeless tobacco
Smoking hazards, but you should not assume that to be the case. You should see your doctor. You may need to see a pulmonary specialist for complete evaluation of this cough. The likelihood is that this cough has a benign cause, but any persistent cough, especially new onset cough, is worrisome and needs to be evaluated.