What Causes COPD?

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Chronic obstructive pulmonary disease (COPD) is an inflammatory, progressive lung disease that constricts the airways and makes breathing difficult. Long-term exposure to harmful substances and irritants—like cigarette smoke, dust, fumes, chemicals, and air pollution—can damage the lungs and airways. Over time, this can lead to chronic bronchitis, emphysema, or both—the two main types of COPD. 

In healthy lungs, the airways are elastic and stretchy and can easily inflate and deflate as you breathe. When you inhale, the airways open up, and the air sacs (alveoli) fill with air, expanding like tiny balloons. When you exhale, the air sacs relax and deflate, moving air out of the lungs. 

When a person has COPD, the airways become narrowed and less air flows in and out, making breathing difficult. This can occur for a number of reasons: 

  • The lungs, airways, and air sacs become damaged and less stretchy 
  • The airways are swollen and inflamed 
  • Mucus clogs or blocks part of the airway 
  • The walls between air sacs are destroyed
Los Angeles Air Pollution Smog

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Types of COPD and Their Causes

There are two main types of COPD associated with damage to the airways and breathing difficulties: 

  • Chronic bronchitis is when the airways (bronchial tubes) are irritated, inflamed, and narrowed after long-term exposure to irritants. The irritation causes mucus to build up, and many people with the disease cough up mucus (phlegm). The combination of mucus and narrowed airways can make breathing difficult for people with chronic bronchitis. 
  • Emphysema is when the small air sacs at the end of the airways (alveoli) are damaged due to repeated exposure to harmful irritants. The damage causes the air sacs to lose their elasticity and shape and become saggy. This makes it harder for the lungs to expand to breathe in and out. 

Both chronic bronchitis and emphysema make breathing difficult and can lead to shortness of breath, a persistent cough, wheezing, and other symptoms. Most people with COPD have both chronic bronchitis and emphysema. 

What’s The Difference Between Chronic Bronchitis and Emphysema?

Chronic bronchitis and emphysema have a few differences, including:

  • Bronchitis affects the airways, whereas emphysema affects the air sacs.
  • Bronchitis causes an excess of mucus in the lungs, leading to chronic cough.
  • Bronchitis is reversible and emphysema is not.

Is COPD Hereditary?

Most of the time, COPD develops due to long-term exposure to cigarette smoke, dust, chemical exposure at work, or air pollution. However, a small number of people have a hereditary genetic disorder that increases their risk of developing COPD. 

A genetic condition called alpha-1 antitrypsin (AAT) deficiency is associated with an increased risk of COPD. AAT is a protein that helps protect the lungs. It is produced in the liver. If your liver does not make enough AAT, your lungs are more vulnerable to damage from smoking and environmental pollutants. 

Up to 5% of people with COPD are thought to have AAT deficiency. AAT deficiency is most common in white people with Northern-European backgrounds but can be found in people of any race or ethnicity. It occurs if you inherited a mutated (changed) AAT gene from both parents. If you inherited a mutated gene from only one parent, you are a carrier for the condition but probably don’t have the deficiency. 

Inherited AAT deficiency is linked to a higher risk of COPD, and a greater chance of developing the disease at a young age. However, not everyone with this deficiency will develop COPD. You can lower your risk by not smoking and taking precautions to avoid exposure to harmful chemicals and air pollution. 

If you have a parent with COPD, talk to your healthcare provider about testing to see if you have inherited AAT deficiency. They can order a blood test to check the level of AAT in your blood. Low levels of AAT may indicate you have the deficiency, and genetic testing may be recommended to find the gene mutation. 

Who Gets COPD?

Some people are more likely to develop COPD than others: 

  • Age: COPD is commonly diagnosed in people who are middle-aged (~40) and older. 
  • Sex: Rates of COPD are higher in people assigned female at birth than in people assigned male at birth. Research suggests people assigned female at birth may be more vulnerable to cigarette smoke and other irritants than people assigned male at birth. People assigned female at birth are also more at risk of early-onset and more severe COPD. 
  • Family history. People with inherited alpha-1 antitrypsin deficiency and smokers with a family history of COPD are at a higher risk. 

Risk Factors

A risk factor is something that increases a person’s odds of developing a disease. COPD risk factors include: 


Smoking is the leading cause of COPD. In fact, up to 90% of COPD cases are linked to cigarette smoking. The more a person smokes—and the longer they smoke—can increase the risk and severity of the disease. Cigarette smoking creates harmful toxins that can weaken the lungs and increase the risk of infection, narrow airways, and destroy air sacs in the lungs, all of which contribute to a higher risk of COPD. 

Secondhand smoke can also increase the risk of the disease, so even non-smokers regularly exposed to toxins in smoke are at risk. Vaping nicotine, marijuana (cannabis), and smoking cannabis flower can also increase a person’s chances of developing COPD.

Occupational Exposure to Irritants 

Exposure to chemicals and fumes of harmful substances at work can damage the lungs and increase your risk of COPD. Long-term exposure to grain and flour dust, coal mine dust, welding fumes, silica, cadmium, and isocyanates (common in auto body paints and varnishes) have all been linked to COPD. Overall, occupational exposure to dust, fumes, vapors, and gasses is associated with a 22% higher risk of COPD. 

Indoor and Outdoor Pollution

Both indoor and outdoor pollutants can irritate airways and harm lung health. Smog (smoke and fog) is outdoor air pollution that contains many particles—some of which may damage the lungs and airways and increase your chances of developing COPD. 

Indoor pollutants such as mold, pet dander, dust mites, asbestos, and combustible pollutants (e.g., firewood smoke, furnaces that use gas or coal) can have detrimental consequences on lung health and lead to the development of COPD. 


Having asthma as a child and/or as an adult is associated with a higher risk of COPD. Research shows that people with asthma have a 12 times higher risk of the disease than those who do not have asthma. 

Childhood asthma has been shown to reduce lung function, which can persist well into adulthood and raise the risk of COPD. Not everyone with asthma will develop COPD. Proper treatment of asthma and not smoking can lower the risk of COPD and other lung health complications.

A Quick Review

COPD occurs when damage from smoking and/or long-term exposure to harmful irritants—chemical fumes, dust, and pollution—causes the airways to become inflamed and swollen, making it hard to breathe. A family history of the disease and personal history of asthma may also increase the risk of the disease. Not smoking and protecting yourself from harmful irritants and chemicals at work and home can help protect your lungs and reduce your risk of COPD. 

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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