COPD Causes and Risk Factors

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

Causes and Risk Factors of COPD
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 for 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.

**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. Three out of four 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.

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 like those of COPD later in life, even if they do not smoke or are not exposed to lung irritants.

Learn more about our ongoing research on COPD.
Changes to lung growth and development: Conditions affecting the lungs when a baby is still in the uterus or during childhood can increase the risk. Examples include smoking in pregnancy or childhood asthma. Air pollution can also limit the growth of a child’s lungs and increase their risk of developing COPD.
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. Other potential genetic risk factors include vitamin D deficiency, and mutations in CHRNA genes . Learn more about AAT deficiency.

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 and men differently?

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

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. Women also have smaller lungs than men do, which may make their airways more prone to narrowing when exposed to irritants.