The 5 most common causes of developing COPD are below:

1.    Cigarette smoke. This is by the far the most common reason people get COPD. You can get it from any tobacco products, like cigar and pipe smoke, especially if you breathe in the smoke.  Smoking is the main cause of COPD and is thought to be responsible for around 90% of cases. The lining of the airways becomes inflamed and permanently damaged by smoking and this damage cannot be reversed. Up to 25% of smokers develop COPD.
2.    Passive smoking. Even if you don’t smoke yourself, just by breathing in second-hand smoke can cause damage to your lungs.
3.    Air pollution. You can get COPD from breathing in chemical fumes, dust, air pollution or toxic substances at work.
4.    Your genes. About 3 in 100 people with COPD have a defect in their DNA. This defect is called alpha-1 antitrypsin deficiency or AAT deficiency. Your lungs don’t have enough of a protein needed to protect them from damage, which can lead to severe COPD. The symptoms normally show before you’re 35 years old. A research study has shown that smokers who have brothers and sisters with severe COPD are at greater risk of developing the condition than smokers who do not.
5.    Asthma. If you don’t treat your asthma, over time you can get lifetime damage and it can develop into COPD.
Some of these risk factors can be avoided by quitting smoking, reducing the amount of pollution we breathe and if we have respiratory problems ensure we medicate and treat them properly. These steps will help to prevent damage to our lungs and help to prevent the development of COPD. Obviously the genetic factor cannot be avoided but only 1% of COPD sufferers have the genetic defect.
References: www.webmd.com and /www.nhs.uk