You light up a cigarette and inhale deeply. That one puff inhales 4,000 to 5,000 different chemicals, when in fact you only really need one – nicotine. Inhaling smoke is one of the fastest and most effective ways to get outside substances into your body, second only to injections. The nicotine in smoke enters the bloodstream through the lungs and takes only about 10 seconds to reach the brain, where it stimulates the release of a neurotransmitter called dopamine. Dopamine focuses the mind, relaxes muscles and produces a pleasurable sensation that is addictive, more so than alcohol, caffeine or even drugs like cocaine and heroin. But nicotine also has a less pleasant side. It can make the heart beat faster, up to 30 percent faster than usual. It constricts blood vessels and narrows them, while blood pressure also rises, to 10 to 15 percent higher than usual. More troublesome is that it can damage the walls of blood vessels and cause atherosclerosis. All of this tends to induce heart disease, and there are other substances in cigarettes that help, such as carbon monoxide. Cigarette smoke contains 600 times the safe level of carbon monoxide, and smokers have 4 to 15 times more carbon monoxide in their blood than non-smokers. Carbon monoxide enters the bloodstream and binds to hemoglobin, making it impossible for the hemoglobin to deliver oxygen, causing a lack of oxygen to the heart and other parts of the body. In order to meet the oxygen supply, the body has to make more red blood cells. With more red blood cells, the blood becomes thicker and more prone to blood clots. Carbon monoxide can also damage the walls of blood vessels leading to atherosclerosis. As a result, smoking increases the risk of heart disease and sudden brain stroke, and the risk of heart attack is five times higher for smokers than for nonsmokers in people under 40 years of age. About a quarter of all deaths from heart attacks are related to smoking. The cardiovascular effects of nicotine and carbon monoxide have other distressing, though not fatal, consequences. Because smoking constricts the blood vessels in the skin, it reduces the blood supply in the skin and makes it prone to aging, which is probably of greater concern to women. For men, the risk of erectile dysfunction (impotence) is increased because smoking damages the blood vessels in the penis and can gradually narrow the arteries connecting the penis, reducing blood flow to the penis and lowering blood pressure. the risk of erectile dysfunction is about 50% higher among men aged 30 to 50 who smoke than among nonsmokers. This risk correlates with the amount of smoking, which is 27% higher for those who smoke 1 to 10 cigarettes a day, 45% higher for those who smoke 11 to 20 cigarettes, and 65% higher for those who smoke more than 20 cigarettes. It is estimated that 23% of erectile dysfunction cases in Chinese men are caused by smoking. Nicotine and carbon monoxide are the colorless gaseous part of cigarette smoke, which also contains irritating gases such as formaldehyde, hydrogen sulfide, and ammonia. They irritate your eyes, nose and throat, making you tear, runny nose and cough. The smoke we see is actually solid particles that don’t burn, mainly tar. If you smoke a pack of cigarettes a day, you will inhale about 200 grams (the equivalent of one cup) of tar over the course of a year. The surface of the respiratory tract is originally covered with cells that grow cilia, and the consistent oscillation of the cilia gradually expels the inhaled particulate matter. However, the toxins in cigarettes prevent these cilia from moving, and as a result of long-term smoking, the throat, trachea and lungs are covered with a dark, sticky layer of tar. Under the stimulation of tar, the respiratory tract secretes mucus. This mucus is also difficult to excrete as phlegm. Tar, dust and mucus accumulate in the lungs, reducing the space in the lungs and causing breathing difficulties. Mucus is also a breeding ground for bacteria and viruses to multiply, making you more susceptible to colds, flu, bronchitis, pneumonia and other respiratory infections; for example, smokers have a four-fold increased risk of getting a lung infection. And once you have contracted a disease, it is not easy to heal because smoking also damages the white blood cells in the lungs that are used to clear pathogens, reducing immunity. Tar contains a large number of harmful substances, including at least 60 known carcinogens and radioactive substances. They come into zero contact with lung cells, and the most immediate, obvious and conclusive consequence is the induction of lung cancer. Prior to the 20th century, lung cancer was an extremely rare disease, with fewer than 80 medically documented cases. But after the 20th century, with the smoking epidemic, cases of lung cancer increased dramatically and year by year, quickly becoming one of the leading causes of death. Now more than one million people worldwide die from lung cancer each year, ranking it as the number one fatal cancer. The lung cancer mortality rate of smokers is more than ten times that of nonsmokers, and 80-90% of lung cancer deaths are related to smoking. The more you smoke, the higher the lung cancer death rate. On average, for every additional cigarette smoked per day, the risk of lung cancer increases by about 50 to 100 percent. The throat and mouth, which are directly irritated by tar, are also susceptible to cancer. Carcinogens enter the bloodstream and reach other parts of the body, where they can induce other cancers, especially in the kidneys, breast, bladder, esophagus, pancreas and stomach. The so-called low-tar cigarettes also contain a lot of carcinogens, and people who smoke low-tar cigarettes often take more puffs or even smoke more cigarettes in order to get high, and the actual amount of tar intake may not be low. The only way to avoid the dangers of cigarettes is to quit smoking and avoid secondhand smoke. According to the World Health Organization, smoking is the second leading cause of death and the largest preventable cause of death. According to several different estimates, the average life expectancy of smokers is reduced by 10 to 17.9 years. Another calculation states that for every cigarette smoked, life expectancy is reduced by 10.7 minutes. When you finish a cigarette, you thereby reduce your life expectancy by even more than the time it takes to smoke a single cigarette.