Are Bronchitis and Pneumonia Dangerous? Both bronchitis and pneumonia share similar symptoms, and it can be hard to tell the difference between them or know what might require medical assistance. A deep cough accompanied by the production of a lot of colored mucus can be a sign of acute bronchitis, but it may also be something else, like a lung infection. If left untreated, both bronchitis and pneumonia can turn into more severe and sometimes ...