My fiance has experiences an unproductive cough for the past 3 winters. It always seems to go away in warm weather, and he says that exercising in the warm weather clears his lungs of pleghm until the next winter. He never experienced it when he lived in warmer parts of the country, and it doesn't seem to be accompanied with any other symptoms like fatigue, chest pain, etc. What could be the cause? Thanks! -Katie
