More than 6 million people across the world die every year from causes directly linked to tobacco use, and about a million more die from second-hand smoke. Overall, the deadly habit kills half of its users.

Smoking is the most preventable cause of premature death in the United States. Mortality among smokers is three times higher than in people who have never smoked.

No organ is spared from the toxins in cigarettes. Not all are equally affected but the smoke is rapidly distributed throughout the body and reaches all tissues, explained Dr. Adam Goldstein, director of Tobacco Intervention Programs at the University of North Carolina School of Medicine. “We now know that smoking is causally related to liver, colon and even prostate cancer, diabetes and macular degeneration, and that quitting is the biggest preventive factor.”

Cigarette smoking is linked to up to 90% of lung cancer deaths in the United States, where it’s the second most common type of cancer and the deadliest. Worldwide, it is the third most common, and also the deadliest.

Over 4.7 billion people are covered by at least one measure to prevent smoking, such as enacting smoke-free laws and providing nicotine-replacement therapy. This is 63% of the world’s population, a rate that has increased four times since 2007.

To identify how exactly a person’s body is harmed by smoking, 24/7 Wall St. reviewed several studies on the effects of smoking and also consulted a medical doctor who conducts research on health policy and disparities in tobacco use and cessation.

Click here to read about what happens to your body when you start smoking.