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Allergic bronchitis is exactly what it sounds like. The bronchial tubes in your lungs are reacting to some type of allergen in your environment. This allergen (whatever it is), is causing the mucus buildup in your lungs. Once you get rid of the allergen (dust, pet dander, pet hair, pollen, etc.), your symptoms should subside. I am no doctor, so I am merely speaking from what I have researched on the subject. If you need a better explanation to ease your mind, contact your pulmonologist and ask whatever questions you can to get an answer you understand. Take care and God Bless.