Tens of millions of Americans have quit smoking cigarettes. The benefits of quitting — no matter what your age — are prodigious. Risks of heart disease and stroke plummet. So does the risk of lung cancer, along with cancers of the mouth, throat, bladder, cervix and pancreas. But can the damage from smoking ever be completely undone? Norman Edelman, chief medical officer of the American Lung Association, explains.

Q: Does your body fully heal after quitting smoking?

A: When you quit smoking, the inflammation in the airways goes down. The little hair-like projections in the airways that we call cilia — which are paralyzed by smoke — begin to work again. So the lungs will get better in weeks to months. Breathing will get better. Exercise capacity will get better. Paradoxically, people find that they cough a little more right after they stop smoking, but that's natural. That's the lungs cleaning themselves out.

But if you've been smoking a long time and have developed COPD [(or, chronic obstructive pulmonary disease)], which includes chronic bronchitis or emphysema, the lungs never totally heal. Chronic bronchitis is an inflammation of the airway. Some of that inflammation can be reversed. But if the inflammation has led to scarring of the walls of the airway, some of that cannot. Emphysema is a disease in which the walls of the fine air sacs of the lung — the place where the lung does its business of exchanging oxygen for carbon dioxide — break down. So tiny little air sacs become bigger ones — and they're less efficient in transporting oxygen. The lung can't grow new walls for these air sacs. The lung loses tiny blood vessels and can't grow new ones. So that's permanent.

[When it comes to cancer], we calculate that the risk for lung cancer probably returns to that of a nonsmoker somewhere between 10 and 15 years after smoking cessation. (We have less data on the [other smoking-related cancers].) But the risk that people have for smoking-related diseases is directly related to the total number of cigarettes they've smoked in their life. We measure that with something we call "pack-years": that's the average number of packs per day multiplied by the number of years they've smoked. The greater the pack-years, the greater the risk. When you're getting up around 50 pack-years and beyond, that's a lot. If people have a lot of pack-years, the risk of, say, lung cancer never goes back down to [the risk of a non-smoker].

There is a famous study that shows that if you quit smoking by age 30, scientists can't show a statistically significant difference in mortality — [that is, when you'll die]. But those data are just mortality statistics. It doesn't mean the lungs are completely normal. Somebody who smoked a lot, even if they quit by 30, probably will have some impairment in lung function, and their exercise capacity might be reduced. Their lungs will always be a little bit more susceptible to other insults, to pneumonia infection for example.

Of course, the way people react to cigarette smoke varies enormously. Everybody has a 90-year-old uncle who smoked all his life and feels fine. And everybody's got a 45-year-old cousin who's dying of emphysema. These two people have reacted to cigarette smoke differently. It's an important scientific question to understand what the differences are, and we're beginning to work on it. Genetics seem to play a role.

成千上萬的美國人已經戒煙.無論你的年齡有多大，戒煙帶來的益處是巨大的.戒煙降低了患心臟病和中風的風險.同時也減少了患肺癌以及口腔癌,喉癌，膀胱癌，子宮頸癌和胰腺癌的風險。但是來自香煙的危害可以徹底消失嗎?美國肺臟協會首席醫務官員諾曼埃德爾曼解釋說.

請問戒煙后您的身體是否完全恢復健康了呢?

當你戒煙的時候,炎癥在氣道上漸漸消失.在氣道上有種象頭發般的突起物質我們稱作纖毛,由于吸煙它被麻痹了,一旦戒煙它又開始工作了.因此肺部功能會在數星期到數月內逐漸恢復.呼吸也會慢慢暢通.運動能力也將一點點好起來.但出人意料的是,人們會發現戒煙后咳嗽卻多了起來,其實這是自然的，因為那是肺部清理垃圾物質.

但如果你吸煙已經有很長時間并且患有慢性阻塞性肺疾病,其中包括慢性支氣管炎或肺氣腫,那么你的肺將再也無法恢復健康.慢性支氣管炎是一種氣道的炎癥.有一些炎癥是可以好轉的,但如果炎癥導致氣管壁留下傷痕的話,那就無法恢復了.肺氣腫是一種肺部纖細的氣孔壁的疾病.這里是肺部進行氧氣和二氧化碳轉換的地方，此時受到了阻塞。因此的纖細的氣孔壁異常擴大，這樣就不能有效的轉換氧氣。而肺部卻無法產生新的氣孔壁。于是肺部就失去了不能再生的微小血管。所以這種疾病是永久性的無法恢復的。

（當肺病轉變成癌癥的時候），我們估算肺癌的風險在戒煙后的10到15年才會轉化成不吸煙者的水平。（我們有不充足的數據[關于其他與吸煙有關的癌癥] ）但是和吸煙相關的疾病的風險是與人們在生活中吸煙的總數直接相關的。我們預測我們所謂的“包年”：是指吸煙者的平均每天的吸煙的包數乘以他吸煙的年數所得的結果。吸煙的包年數植越大，患病的風險就越大。當你吸煙時間等于或大于50包年時，那說明你吸煙時間很長了。有很多包年煙齡的吸煙者所面臨的肺癌的高風險使他們再也無法回到不吸煙者所面臨肺癌低風險的范疇。

有項著名的研究表明，如果你30歲戒煙的話，科學家無法說明死亡率統計的明顯差異。（也就是說，什么時候你會死）。但是這些數據僅僅是死亡率的統計。并不意味著肺部功能是完全正常的。一些人吸煙時間較長，即使30歲就戒煙了也可能他的肺部功能留下了損傷，他的運動能力也會下降。他們的肺部也會因此更容易受到別的疾病的影響，如肺炎等肺部傳染病。

當然，人們對吸煙后產生的反應也是各不一樣的。大家有個90歲的叔叔他吸煙吸了一輩子，但感覺一直很好。而大家有個45歲的兄弟卻因為吸煙死于肺氣腫。這兩個人對于吸煙有著不同的生理反應。對于這種差異這是個十分重要的科學議題，我們正開始研究這些差異產生的原因。而遺傳學仿佛起了關鍵的作用