It is now well documented that secondhand cigarette smoke can cause or aggravate diseases in others around you. These include respiratory problems and allergies. Co-workers, spouses, children, even pets can be affected. Tobacco smoke contains about 4,000 chemicals. Further, many of the chemicals in cigarette smoke have been shown to cause cancer.
Quality of life is one of the biggest reasons.
Everyone has to die someday. You'll reduce the risk of heart attack, stroke, lung cancer, leukemia, and many other cancers as well. Within just 20 minutes of quitting, your blood pressure and pulse rate drop to normal, and the body temperature of your hands and feet increases to normal. In 8 hours, the oxygen level in your blood returns to normal. In 24 hours, your chance of a heart attack decreases.