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.

成千上万的美国人已经戒烟.无论你的年龄有多大，戒烟带来的益处是巨大的.戒烟降低了患心脏病和中风的风险.同时也减少了患肺癌以及口腔癌,喉癌，膀胱癌，子宫颈癌和胰腺癌的风险。但是来自香烟的危害可以彻底消失吗?美国肺脏协会首席医务官员诺曼埃德尔曼解释说.

请问戒烟后您的身体是否完全恢复健康了呢?

当你戒烟的时候,炎症在气道上渐渐消失.在气道上有种象头发般的突起物质我们称作纤毛,由于吸烟它被麻痹了,一旦戒烟它又开始工作了.因此肺部功能会在数星期到数月内逐渐恢复.呼吸也会慢慢畅通.运动能力也将一点点好起来.但出人意料的是,人们会发现戒烟后咳嗽却多了起来,其实这是自然的，因为那是肺部清理垃圾物质.

但如果你吸烟已经有很长时间并且患有慢性阻塞性肺疾病,其中包括慢性支气管炎或肺气肿,那么你的肺将再也无法恢复健康.慢性支气管炎是一种气道的炎症.有一些炎症是可以好转的,但如果炎症导致气管壁留下伤痕的话,那就无法恢复了.肺气肿是一种肺部纤细的气孔壁的疾病.这里是肺部进行氧气和二氧化碳转换的地方，此时受到了阻塞。因此的纤细的气孔壁异常扩大，这样就不能有效的转换氧气。而肺部却无法产生新的气孔壁。于是肺部就失去了不能再生的微小血管。所以这种疾病是永久性的无法恢复的。

（当肺病转变成癌症的时候），我们估算肺癌的风险在戒烟后的10到15年才会转化成不吸烟者的水平。（我们有不充足的数据[关于其他与吸烟有关的癌症] ）但是和吸烟相关的疾病的风险是与人们在生活中吸烟的总数直接相关的。我们预测我们所谓的“包年”：是指吸烟者的平均每天的吸烟的包数乘以他吸烟的年数所得的结果。吸烟的包年数植越大，患病的风险就越大。当你吸烟时间等于或大于50包年时，那说明你吸烟时间很长了。有很多包年烟龄的吸烟者所面临的肺癌的高风险使他们再也无法回到不吸烟者所面临肺癌低风险的范畴。

有项著名的研究表明，如果你30岁戒烟的话，科学家无法说明死亡率统计的明显差异。（也就是说，什么时候你会死）。但是这些数据仅仅是死亡率的统计。并不意味着肺部功能是完全正常的。一些人吸烟时间较长，即使30岁就戒烟了也可能他的肺部功能留下了损伤，他的运动能力也会下降。他们的肺部也会因此更容易受到别的疾病的影响，如肺炎等肺部传染病。

当然，人们对吸烟后产生的反应也是各不一样的。大家有个90岁的叔叔他吸烟吸了一辈子，但感觉一直很好。而大家有个45岁的兄弟却因为吸烟死于肺气肿。这两个人对于吸烟有着不同的生理反应。对于这种差异这是个十分重要的科学议题，我们正开始研究这些差异产生的原因。而遗传学仿佛起了关键的作用