More times than not, doctors see that the cause of bronchitis is due to the same virus (es) that give you the common cold or the flu. However, sometimes bacteria is to blame. In both of these cases, as your body is fighting off the germs, your bronchial tubes will swell up and begin to make more mucus. This means that you will have a much smaller opening for air to flow, and this can make it hard for you to breathe. If any of these circumstances describe your situation, then you will have a larger chance of catching bronchitis: • You have a weaker immune system, this is highly common in older adults, babies, and young children • You smoke or happen to live with a smoker • You work around substances that can bother or irritate your lungs, such as chemical fumes or dust • You live or have traveled to a place with poor air quality or that is heavily polluted