The human lungs are complex and highly evolved organs whose performance is life-sustaining. And while medical science has over decades developed a deep knowledge of their function and related diseases, important research continues relentlessly and new insight is gained every day.
The factors causing lung disease are numerous and interrelated, including heredity, overall health, geography, lifestyle habits such as smoking, exposure to second hand smoke, air pollution and more.
In short, smoking, exposure to radon and exposure to second-hand smoke are the most significant, easily assessed factors in determining your risk.
Alveoli
Tiny, spherical outcroppings of the bronchioles. The alveolar membrane is the gas-exchange surface. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveoli is taken up by the blood in the alveolar blood vessels, to be transported to all the cells in the body.
Bronchioles
Smaller passageways that extend to from the bronchi to the alveoli.
Bronchi
These are the large passageways that extend from the trachea into the lungs.
Trachea
The bony tube that connects the nose to the mouth and then to the lungs, allowing the passage of air. The trachea is also known as the windpipe
For more information on indoor radon, visit the EPA's Consumer's Guide to Radon.
Chronic Cough
A cough lasting a month or longer is chronic. It's an important signal indicating problems with your breathing system, regardless of age.
Shortness of Breath
Shortness of breath continuing after a brief rest following normal exercise - or develops with little or no exertion - isn't normal. Labored breathing, the sensation of difficulty in drawing air or exhaling is also a warning sign.
Chronic Mucus Production
Mucus, also called sputum or phlegm, is produced by the airways as a defense against infections or irritants. If your mucus production continues for a month, it may indicate lung disease.
Wheezing
"Noisy breath" or wheezing indicates that something unusual is blocking your lungs' airways or narrowing them unnaturally.
Coughing Up Blood
Blood being coughed up may originate from your lungs or upper respiratory tract. Whatever the source, it signals a health problem.
Chronic Chest Pain
Unexplained chest pain lasting a month or more - especially if it worsens with breathing or coughing - can also be a warning sign. The degree of pain may vary over a wide range, but its persistence over a month or more is a key factor as it relates to possible lung disease.



