COPD Causes and Risk Factors

Cigarette smoking is the most common cause of COPD in the United States. Long-term smoking or exposure to breathing in tobacco smoke or pollutants in the air damages the lungs and airways.

Causes and Risk Factors of COPD (3:26)
Learn about NHLBI research to help understand why some people get COPD or get more severe COPD than others.

How COPD affects the lungs

In healthy lungs, the air that is breathed in travels down bronchial tubes, which often branch many times into thousands of smaller, thinner tubes called bronchioles. These tubes end in bunches of tiny round air sacs called alveoli, which are elastic or stretchy.

Learn more about how air flows through the airways in our How the Lungs Work topic.

In COPD, less air flows in and out of the airways because of one or more reasons:

The airways and air sacs lose their elastic quality.
The walls between many of the air sacs are destroyed.
The walls of the airways become thick and inflamed.
The airways make more mucus than usual and can become clogged.

Figure A shows the location of the lungs and airways in the body. Figure B shows lungs damaged by COPD. — **Normal lungs and lungs in a person who has COPD.** Figure A shows the location of the lungs and airways in the body. Figure B shows lungs damaged by COPD

What raises your risk of COPD?

The following may raise your risk of COPD.

Smoking: This is the main risk factor for COPD. Most people who have COPD smoke or used to smoke. People who have a family history of COPD are more likely to develop the disease if they smoke.
Other lung irritants: These may include long-term exposure to air pollution, chemical fumes and dust from the environment or workplace, smoke from home cooking and heating fuels without ventilation, and secondhand smoke, which is smoke in the air from other people smoking.
Changes to lung growth and development: Diseases affecting the lungs when a baby is still in the uterus or during childhood can increase the risk.
Infections: Conditions such as HIV and tuberculosis can raise your risk.
Age: Your age may play a role in COPD risk if you have other risk factors, such as smoking. Most people who have COPD are at least 40 years old when symptoms begin.
A condition that runs in families, called alpha-1 antitrypsin (AAT) deficiency: If you are born with this condition, smoking or long-term exposure to fumes or dust can lead to lung damage and COPD. AAT deficiency can also raise your risk for developing COPD at a younger age.
Asthma: About 1 in 5 people who have COPD also have asthma, a lung disease that causes swelling and narrows the airways.

Research for your health

NHLBI-supported research found that having smaller airways for your lung size can also raise your risk for COPD. Smaller airways can prevent your lungs from working as well as they should. Lung function declines naturally as we age so people with smaller airways may develop symptoms similar to those of COPD later in life, even if they do not smoke or are exposed to lung irritants.

Learn more about our ongoing research on COPD.

Fact sheet

COPD Learn More Breath Better: Are You at Risk?

Learn more about the risk factors for COPD.

View the fact sheet

How does COPD affect women differently than men?

COPD affects both men and women. However, COPD may affect women differently than men.

Compared with older men, older women may be more likely to experience serious symptoms of COPD, such as severe shortness of breath, even when smoking less during their lifetime than men.
Women who have COPD are more likely to have symptoms at younger ages and be hospitalized for symptoms than men who have COPD.
Women who have COPD tend to smoke less and have lower body mass index (BMI) than men who have COPD.

The reason for the differences in COPD between men and women is not known. Researchers think the cause may be related to hormones or other physiological differences, or differences in biology, of men and women. Women have smaller lungs than men, which also may cause their airways to narrow more than men.