Smoking
This one is a given. Since the 1970s people have been made aware of the harm of smoking cigarettes. In fact, there are a total of 70 chemicals found in cigarettes that can cause cancer. Don’t think you’re safe if you don’t smoke though. Secondhand smoke can also cause cancer. “Nonsmokers who are exposed to secondhand smoke at home or at work increase their risk of developing lung cancer by 20-30%.” The Centers for Disease Control and Prevention said.