Bronchitis causes from viruses and bacteia result in cold or flu and if stay for long then it is bronchitis. Your lungs has smaller openings for air to flow which can make hard to breathe. Weaker immune system, old age, ongoing diseases have more chances of bronchitis. Living poor air quality or pollution causes bronchitis.
Chest congestion, cough bringing lot of mucus that's white, yellow or green, shortness of breath and whistling sound are symptoms of bronchitis.