MONICA SCHROEDER / SCIENCE PHOTO LIBRARY MONICA SCHROEDER / SCIENCE PHOTO LIBRARY
Illustration depicting bronchitis, a disease in which the mucous membranes of the bronchi (airways in the lungs) become inflamed and clogged with mucus. There are two types: acute and chronic. The former is usually the result of a cold or viral infection, and the latter is often the result of smoking tobacco or long-term exposure to air pollution.
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