Cigarettes contain various harmful chemicals, most likely things you didn't even think were in cigarettes. Some of these include rat poison, toilet cleaner, candle wax, and battery acid...
Heart Disease or Heart Cancer
Cigarettes can lead to various types of cancers. The risk of developing heart disease is tripled, and other diseases greatly increased.
Smoking can also cause bad, smoke smelling breath. It may also lead to a smoker's cough which is created when the cilia are plastered down by tar forcing the body to send out mucus through a cough. Smoking also leads to premature aging. Now that you know all of this, please do not smoke.