Phlegm is a form of respiratory mucus produced by the lungs. The airways between the larynx and the respiratory bronchioles are lined by columnar epithelium over which an airway surface liquid (ASL) ...
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What causes brown mucus?
Medically reviewed by Amelia MacIntyre, DO Smoking can lead to brown mucus due to tar build-up in the lungs. Inhaling pollutants and toxins can cause brown mucus. Lung infections from bacteria and ...
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