Smoking
Though the tobacco industry tried to cover this one up, we’ve known for years that tobacco smoke has at least 70 cancer-causing chemicals inside. And it’s not just smokers who are affected — people who inhale secondhand smoke can develop deadly forms of cancer too. The Centers for Disease Control and Prevention says: “Nonsmokers who are exposed to secondhand smoke at home or at work increase their risk of developing lung cancer by 20-30%.” People who chew their tobacco are at increased risk too.