MONICA SCHROEDER / SCIENCE PHOTO LIBRARY MONICA SCHROEDER / SCIENCE PHOTO LIBRARY
Illustration of chronic obstructive pulmonary disease, a common lung disease where breathing is difficult. There are two main forms of COPD: Chronic bronchitis, whose symptoms include a long-term cough with mucus) (inset bottom) and emphysema (the gradual breakdown of the lungs) (inset top). Most people with COPD have a combination of both forms. COPD is caused by noxious particles or gas, most commonly from tobacco smoking, which triggers an abnormal inflammatory response in the lung.
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