Smoking

So when you puff on a cigarette what, exactly, is going into your lungs?

Nicotine This is the addictive drug in cigarettes. It is a stimulant so it makes the brain work faster. Nicotine by itself isn't actually that harmful. It's all the other stuff that you inhale with it.
Tar This is the same stuff that they put on roads. It is a smelly, sticky black substance that collects in the lungs of smokers. Obviously, the lungs will not work as efficiently when full of tar. The picture shows the lungs of a smoker and a non-smoker.
Carbon Monoxide This is a very poisonous substance. It affects how well your blood carries oxygen. Oxygen is needed for respiration to smokers often feel tired. If a woman smokes when pregnant then the unborn baby will get less oxygen and so will not develop as well.
Other Chemicals Many of the chemicals in cigarette smoke can cause cancer. This is a very nasty disease where cells in our bodies grow uncontrollably. Cancer is not the only serious disease you can get from smoking. There are many others.

So why do people smoke?

The fact is that most smokers wish they didn't smoke. Stopping smoking is incredibly difficult to do. The trick is not to start in the first place.

REMEMBER

Nicotine is the addictive substance in tobacco smoke.
Tobacco smoke contains carcinogens.
Tobacco smoke also contains carbon monoxide which reduces the oxygen-carrying capacity of the blood. In pregnant women this can deprive a foetus of oxygen and lead to a low birth mass.