Smoking has been quite prevalent in most countries of the world. Smoking is practised since 2000BC. There are 120 million smokers in India alone which accounts for 12% of smokers in World. According to an estimate, more than 1 million smokers die in India.
According to another estimate, approximately 35 million people are active smokers in USA.



1. EMPHYSEMA
 Emphysema is abnormal dilatation of the lungs. Alveoli are balloon like sacs present in lungs which help in intake and out take of air.

In emphysema these alveoli are damaged. Smoking being one of the main reasons.

When alveoli are damaged, there is an inflammatory reaction in lungs which leads to following changes :-

- Excess mucus production which leads to narrowing of trachea and bronchi (wind pipes)
- Abnormal increase in size and number of smooth muscle cells.
- Increased amount of inflammatory cells like macrophages, neutrophils, lymphocytes, B cells and T cells. 

2. ASTHMA
Smoking is a cause of non atopic asthma. 
Tobacco smoke can lead to irritation of the lung tissues leading to a harmful reaction which is called Type I Hypersensitivity. This leads to an inflammatory reaction called asthma.

3. CHRONIC BRONCHITIS
It is a condition in which a person has cough with sputum for at least three months in at least two consecutive years. Smoking is one of the main factors causing Chronic Bronchitis.

                   Smoking
                         ⬇
                   Inflammation
                         ⬇
   Increased mucus production than required
                         ⬇
  Thickness of mucus gland layer increases
                         ⬇
  Diameter of airway in lungs decreases
                         ⬇
          Productive cough
                         ⬇
       Less oxygen supply to body
                         ⬇
         Right sided heart failure

4. COPD ( CHRONIC OBSTRUCTIVE LUNG DISEASE ).
 It is caused by Emphysema and Chronic bronchitis together. There is blockage of airflow and beathing becomes difficult.
5. LUNG CANCER
 




About 80% of lung cancers occur in active smokers or those who stopped recently.

Cancer of lung occurs most often between ages 40 and 70 years.

Lung cancer also occurs in people who do not smoke but are constantly exposed to tobacco smoke. Each year about 3000 non smokers die of lung cancer.

Types of lung cancers which occur due to smoking are:
1. Squamous cell carcinoma :- In this condition, cells of lungs show abnormal growth which eventually leads to narrowing of the airways leading to difficulty in breathing and lung collapse.

2. Small cell carcinoma :-  This type of cancer is strongly related to lung cancer. In this there is lung damage as well as certain hormones are abnormally secreted which leads to following changes :-

- Low blood calcium level.

- Increased body water and sodium concentration leading to edema (swelling) and a condition called Cushing syndrome.