Smoking and Respiratory Diseases Smoking is directly responsible for the majority of lung cancer cases (87 percent), emphysema cases, and chronic bronchitis cases. Why Quit Smoking? You know you should quit smoking. But you just haven't gotten around to it yet. Here are some reasons to help you commit to quitting. How to Quit Smoking, Again Fewer than a quarter of those who attempt to quit are able to make it beyond three months before resuming smoking. Women usually find it harder to quit than do men, even though women have a higher risk of smoking-related diseases. The following suggestions can help you kick the habit, again, for good.