Chronic obstructive pulmonary disease, or COPD, is an inflammatory lung disease mainly caused by long-term exposure to irritants, such as cigarette smoke, air pollution, and chemical gases. In rare cases, the disease also may result from a hereditary lung condition.
In COPD, the airways become chronically blocked. This blockage causes several symptoms, including a persistent cough, wheezing, and shortness of breath.
There are two main types of COPD: emphysema and chronic bronchitis. In people with emphysema, the walls of the alveoli — the tiny air sacs where oxygen is exchanged — are damaged and lose elasticity. As a result, the airways and alveoli over-expand, causing the airflow in and out of the lungs to decrease.
In chronic bronchitis, the lung airways are constantly irritated and inflamed. Over time, this constant irritation causes the airways to become enlarged and promote the production of sticky mucus, which may block the narrowed airways. Patients with this type of bronchitis tend to develop a chronic cough that manifests whenever they try to clear their airways.
The causes of COPD are not fully understood. However, long-term exposure to lung irritants is known to damage the lungs and the airways.
Long-term tobacco smoking is the main cause of COPD in developed countries. This includes secondhand smoke, which is a combination of cigarette smoke breathed out by smokers and smoke from the burning end of cigarettes.
Some chronic smokers may not show overt signs of lung disease, while others may go on to develop less common lung conditions. As such, COPD is not always clinically evident, and some patients may be initially misdiagnosed until undergoing a deeper medical evaluation.
Cigarette smoke contains high concentrations of oxidants — harmful molecules that can cause oxidative stress in tissues and organs — that are known to induce inflammation in the lungs and airways. Of note, oxidative stress is a form of cellular damage resulting from a disequilibrium or imbalance between the production of oxidant molecules and the body’s antioxidant defense mechanisms that eliminate them.
People also are at risk of COPD if they have longterm exposure to secondhand smoke. According to the Centers for Disease Control and Prevention, secondhand smoke contains more than 7,000 chemicals, hundreds of which are toxic to people.
Pipe, cigar, and marijuana smokers also may be at risk of developing COPD.
There are other factors, such as air pollution, that play a role in the development of COPD. Long-term exposure to dust, chemical gases, and vapors in the workplace may cause irritation and inflammation in the lungs.
In developing countries, COPD often occurs in people living in poorly ventilated homes who are exposed to fumes from burning wood or fuel for cooking.
Yet, the mechanisms underlying air pollution as one of the causes of COPD are unclear. Further study also is needed on effects of air pollution on COPD.
Rarely, in about 1% of patients, COPD results from a deficiency in a protein called alpha-1-antitrypsin (AAT). This protein is produced by the liver and then enters the bloodstream in order to travel to the lungs. Once there, AAT protects them against damage caused by irritating substances, such as cigarette smoke.
If AAT fails to reach its final destination, or is faulty, the lungs become unprotected and the alveoli are destroyed. AAT deficiency is a hereditary condition caused by mutations in the SERPINA1 gene, which provides instructions to make AAT.
People with asthma, a chronic inflammatory disease that causes the lung airways to become narrower, also may be at risk of developing COPD when the disease is not managed properly. Both diseases also may coexist in the same patient, giving rise to a condition known as asthma-COPD overlap syndrome (ACOS).
Persistent asthma can lead to COPD independently of smoking, but smoking increases the risk of COPD in people with asthma.
Last updated: April 30, 2021
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