Smoke may be great for grilling and haunted houses, but you don’t have to be the Marlboro man to know what kind of damage smoking can do to your lungs.Pumping smoke down your airways makes you eight years older—putting you at risk for lung diseases like emphysema, cancer and bronchitis. Just two months of being smoke-free can make you one year younger. After five years of smoke-free living, a former smoker can regain seven of the eight years lost to smoking.The Science of Quitting SmokingWe’re a society that doesn’t like quitters—not in sports, school or food-eating contests. So it’s against our nature to give up something we’ve started—even cigs.One of the toughest parts of quitting is that cigarettes are both psychologically and physiologically addictive. From the physiological end, it seems the release of dopamine—a naturally occurring substance in your body that dulls pain and causes pleasure—is triggered when you’re smoking.You get used to the elevated dopamine levels, so when you don’t smoke, you crave the cig with no explanation as to why (it’s almost like when a pregnant woman craves pickles). Luckily, those dopamine levels don’t stay elevated all the time, and if you can quit, you can switch your dopamine level back to normal.Psychologically, smoking becomes a behavioral addiction—you have a cig with a beer, after dinner or sex. And you get used to the feeling of picking something up and putting it in your mouth.The hardest part of quitting comes the first week. You feel cravings and are sluggish. You start producing and expelling a lot of gunk from the lining of your lungs. But all that subsides after a few weeks, if you can push through.Quitting and Weight GainOne of the biggest concerns with quitting smoking is the potential weight gain. On average (and without the walking), men gain 10 pounds after quitting, and women about eight.Six months later, the typical woman is just two pounds heavier than when she was smoking, but those women and men who use a plan of walking and weight lifting are actually an average of six pounds lighter than the day they quit.Though the dangers of smoking far outweigh the dangers of this additional weight, you can prevent weight gain during the quitting process.Walking helps. Chewing sugarless gum eases oral cravings. Put a rubber band around your wrist so you have something to do with your fingers besides pick up baby back ribs. Concentrate on fruit, vegetables and unbuttered popcorn (low-fat snacks), with a few healthy-fat snacks like six walnuts along with the fruit.If you can make any change that’ll improve your health and make you live younger, it’s this one. For once in your life, be a quitter—and be proud of it.QUIZ: Are You Getting Enough Exercise?Secondhand SmokeSecondhand smoke is one of the few actions another person can do that can contribute to your aging process. Spending an hour in someone else’s smoke is like smoking four cigarettes yourself.In other words, for every cigarette that a smoker smokes, you’re inhaling about a third of it yourself. Just look at the consequences: Spending four hours a day in a smoking environment can make you as much as 6.9 years older.That’s all the more reason that if you live with a smoker, you have to encourage that smoker to quit. It’ll help your partner, and not to mention, you!