Let us see what happens in our body when a cigarette is lit.
When a cigarette is lit, the tobacco burns and smoke is produced. this smoke is taken in by our body when we inhale. The harmful substances in teh smoke are absorbed by the lungs and enter the blood stream.
One of eh harmful substances that enter the blood stream is carbon monoxide.
Carbon monoxide combines with the red blood cells, preventing them from carrying oxygen. So, a smoker has less supply of oxygen in his red blood cells. As a result, his body's immunity is weakened. His body becomes easily affected by common colds and flu.
Tar, another harmful substance, sticks to the lungs and prevents them from working properly.