What is smoking? Smoking is an unhealthy behavior that can become an addiction. Smoking is the most important preventable cause of premature death in the United States, according to the American Heart Association. Smoking includes all forms of smoking, such as cigar smoking, cigarette smoking, pipe smoking, and exposure to secondhand smoke. All forms of smoking are harmful and there is no form of safe or safer smoking. For example, smoking mentholated, natural, or low-tar, low-nicotine cigarettes does not lower the risk of serious complications of smoking. Smoking causes or worsens many diseases and damages almost every tissue and organ in the body. Smoking causes the vast majority of cases of lung cancer and causes or exacerbates many other diseases, such as lung diseases, diabetes, cancer, and diseases and conditions of the cardiovascular system including hypertension, blood clots, high cholesterol, and stroke. Smoking also increases the risk of certain complications of pregnancy and sudden infant death syndrome (SIDS). Smoking tobacco exposes you to over 4,000 chemicals, many of which are toxic. Toxins found in cigarettes include formaldehyde and cyanide. Another harmful substance in cigarettes and tobacco is nicotine. Nicotine is an addictive drug with serious side effects. Smoking also exposes you to carbon monoxide, which lowers the level of oxygen in the blood. People close to a smoker are exposed to the same toxins and can experience similar complications of smoking due to the inhalation of secondhand smoke. Because of the addictive nature of smoking, quitting is a difficult challenge. However, quitting smoking is one of the best things you can do for yourself, your health, and your family and friends. Quitting smoking improves the health of the lungs and increases respiratory capacity. This is the ability to take in sufficient amounts of oxygen. People who quit smoking experience a rapid increase in oxygen levels in the blood, less shortness of breath with activities, feel less fatigue, and have more energy. Another important benefit of smoking cessation is the improvement in vital signs including a decrease in high blood pressure and pulse. The amount of carbon monoxide in the blood also drops after smoking cessation. Because smoking constricts blood vessels and negatively affects circulation, smoking cessation is very beneficial for people who have other serious diseases that affect blood vessels and circulation, such as diabetes, congestive heart failure, and other cardiovascular diseases.