In the overwhelming majority of chronic obstructive pulmonary disease (COPD) cases, the main cause of lung damage is smoking tobacco. A classic COPD patient is a person around the age of 50 or 60 who has smoked one or more packs of cigarettes per day for over two decades (20 pack years). Although most studies have pointed out the harmful effects of cigarette smoke, recent research has noted that cigar and pipe smoke also appear related to COPD. In addition, recent studies have suggested that breathing in someone else’s smoke (called side-stream or second-hand smoke) can eventually damage the lungs of non-smokers and increase their risk of developing COPD.

Patients who have both COPD and asthma usually cause the serious lung damage associated with severe COPD by continuing to smoke. Asthma is very rarely capable of damaging the lungs as severely as the combination of smoking and COPD. Although coexistent asthma and COPD can result in a more severe overall respiratory condition, the two conditions are usually treated independently.

COPD is typically the result of one of two different lung conditions – emphysema and chronic bronchitis – and the causes of these two conditions can also lead to COPD:

• Chronic bronchitis is often the result of smoke that has irritated and damaged the mucous glands, airways and hair-like cells (cilia) that normally wave toxins out of the lungs.
  
  
• Emphysema is often the result of smoke that has triggered the immune system to produce more harmful enzymes. Although these harmful enzymes are normally prevented from causing any significant damage by a protective protein, smoking reduces the protein’s protective effect. Even if someone has plenty of the protein in their system, smoking generates certain substances that keep the protective protein from doing its job.

Although the main cause of COPD is tobacco smoke, there are also genetic causes. For example, some people’s lungs are more sensitive to irritants, making it more likely that they will develop COPD. Other people are born with an abnormally low level of protective protein (alpha-1-antitrypsin), so there is less protection from harmful enzymes and a greater chance of developing emphysema.

In addition to smoking and genetic factors, the following people are particularly vulnerable to COPD:

• People who frequently inhale many airborne irritants (e.g. air pollution and occupational exposure to industrial pollution)
  
  
• People exposed to excessive fungi/mold
  
  
• People with few antioxidants (e.g., vitamin C) in their diet
  
  
• Older people

Obesity has been identified as a risk factor for chronic bronchitis, and low body weight has been linked to emphysema. Furthermore, some experts believe that COPD can be a consequence of childhood respiratory infections and recurrent upper respiratory infections (e.g., getting pneumonia year after year). However, researchers are still working to understand the role that infections may play in the development of COPD.