The smoke consists of various gases and particulates like nicotine, water and tar. Tar, which contains numerous cancer-causing carcinogens, is what remains of the smoke particles once the nicotine and water have been removed from the burning tip. This tar, and compounds like carbon monoxide, are what's dangerous. They greatly increase your risk for a number of conditions that threaten your life and quality of life. This process is known as atherosclerosis.
Smoking leads to premature atherosclerosis, which in turn can lead to heart attacks and strokes.
If you're a smoker in your 30s or 40s, you're more likely to die of a heart attack than cancer. And you're five times more likely to die from one than a non-smoker. If you're a male smoker between the ages of 35 and 64, your chance for a stroke is increased almost four times. If you're a woman, it's nearly five times. These deaths are linked to the carcinogens in the smoke.