Chronic obstructive lung disease(COPD) is caused by long-term exposure of lung tissues to any chemical irritant or a long-term history of smoking. It can also be caused due to secondhand smoking or passive smoking, where one gets exposed to cigarette smoke caused by another person's smoking and inhales it. It is due to the harmful chemicals present in cigarette smoke that destroy the lung lining. It leads to emphysema and chronic bronchitis. Most of the time, COPD is not genetic, it is caused due to tobacco and chemical irritants of the smoke. But in some cases, it can be genetic, as people born with alpha-1-antitrypsin deficiency cannot produce the protein that can prevent damage to the lungs, and hence are more prone to acquire COPD. Chronic bronchitis is a condition where the bronchioles or oxygen-carrying lung tubules that carry air to and fro undergo inflammation and thickening leading to chronic cough with excess mucus secretion. Emphysema is a condition where the alveoli, which are the end of the smallest air passage are destroyed as a result which there is a reduced flow of oxygen to the lung tissues and excess carbon dioxide accumulated in the lungs leading to breathing difficulties. People with COPD are at increased risk of acquiring lung cancer due to damage to the lung tissue which can be fatal if left untreated for a long time. There is no cure for COPD, nor can it be reversed. However early diagnosis and quitting smoking can help slow down the process and relieve all chest congestion symptoms.