Smoking is harmful to the human body because some of the chemicals it contains can cause chronic airway inflammation and even malignant tumors in the lungs. How long it takes to be successful in the process of quitting smoking varies from person to person. It can take anywhere from three months to a year, or even longer to complete. Because some people are weak-willed and tend to relapse in the process of quitting smoking, it takes longer. Some people are more self-disciplined and can easily quit smoking in a short period of time. But most people who finish the process of quitting smoking are more likely to be more addicted to smoking than before if they return to smoking, so it is more troublesome to quit. According to clinical statistics, the longer you quit smoking, the lower the probability of relapse.