Multiple things; mostly the chemicals that are added by the tobacco companies to enhance their products. Plus the fact when you inhale anything into your lungs you irritate them - causing damage.
Nicotine
Over 1,000 different substance all in them
carcinogen
The adds by cigarette companyhave been banned as it causes cancer and to warn the public.
Approximately 15 to 30 of cigarette smokers develop cancer.
While it's hard to determine exactly what's in tar, it's clear that it causes most of the bad health effects of tobacco: Cancer.
A somewhat satirical synonym for cigarette is cancer stick.
because a PART of our body gets rotten then it causes us cancer.
Cigarette produces a certain amount of a substance called tar in our lungs which causes cancer. After an year this tar becomes so much in amount that it can cause any disease in our body
Lung Cancer or Heart Disease or Strokes and a variety of other cancers
That would be the nicotine in the cigarette. this answer sucks
cancer sticks