After a cold or flu, the two main branches of your respiratory tract, your bronchi, often become irritated and inflamed, says Alan Brauer, M.D., director of TotalCare Medical Center in Palo Alto, California, one of the nation’s oldest clinics to combine mainstream and complementary medicine. That, in turn, impairs the ability of the tiny hairs that line the bronchi (cilia) to sweep mucus and other debris out of your respiratory tract. With your bronchi inflamed and your cilia handicapped, the only way your body can keep your bronchi clear is to cough. Hence, bronchitis, which may last a week or two.