First, the bad news: Lung cancer is the most common cause of cancer death for American adults—and smoking is to blame for at least 85 percent of all lung cancer deaths.

Now, the good news: If you give up smoking, your health will start to improve in just a few weeks. If you quit forever, your risk of lung cancer—and dozens of other diseases and cancers—will drop significantly in the next few years.

The main ingredient in cigarette smoke is nicotine, the substance smokers become addicted to. When you smoke, you also inhale poisonous gases, such as carbon monoxide, and more than 60 cancer-causing chemicals, including cyanide and benzene. No wonder smoking is dangerous!

Even before lung cancer appears, smokers often develop chronic bronchitis, which produces the familiar smoker’s cough, and emphysema, which slowly destroys the ability to breathe. Because these two conditions so commonly occur together, they’re often referred to collectively as chronic obstructive pulmonary disease, which leaves sufferers literally gasping for breath.

Active “puffers” are not the only ones who suffer from smoking. Exhaled smoke and burning cigarettes create secondhand smoke. It, too, causes lung cancer when inhaled by even healthy nonsmokers. Children whose parents smoke are more likely to develop pneumonia, bronchitis, ear infections and asthma. What’s more, pregnant women who smoke increase their chances of miscarriage and stillbirth.

Despite these scary facts, there is some good news to be found: Since 1965, the number of adult smokers has been cut in half. And each year, more than half of all daily smokers try to quit. If you still smoke, isn’t it time you joined them?