Repeated infections of the bronchi and bronchioles thicken and distort the lining of these tubes, which are also narrowed and obstructed by oversecretion of mucus and excessive contraction of muscles in their walls. Over the years, the amount of sputum gradually increases, and coughing begins to occur throughout the day. Breathlessness and wheeziness gradually become increasingly troublesome. In the early stages, only bad colds or attacks of influenza cause flare-ups. Eventually, though, every minor head cold brings on a severe attack.
Many sufferers have several flare-ups every winter.
In the late stages, coughing, breathlessness and wheezing are severe and nearly continuous. Around a million others have the disease, many without realising it. Smoking is the main cause. Among major diseases to which chronic bronchitis can lead are pulmonary hypertension, emphysema and right-sided heart failure. If infection spreads into the alveoli, the result is likely to be pneumonia.