No matter what level of exposure of smoke you have, your lung cells know it and they are responding.

无论你暴露在何种程度的烟雾环境中，你的肺部细胞都知道并且会做出反应。

youdao

There is no safe level of exposure to second-hand tobacco smoke.

关于二手烟草烟雾，不存在安全接触水平。

youdao

"When you look at the biology, there is no safe level of exposure to tobacco smoke," he says.

他还说：“当你看了生物学以后就会发现，任何级别的烟雾含量都是不安全的。”

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But clearly there is no such thing as a safe level of cigarette smoke exposure.

VOA: special.2009.06.03

"The people that are at the highest level of passive smoke are actually the ones reporting exposure in their own homes.

VOA: standard.2010.06.15

To accurately assess the level of second-hand smoke exposure, researchers tested for cotinine, which is produced when nicotine is metabolized.

VOA: standard.2010.06.15

Her stance was backed by the British Heart Foundation and Cancer Research UK, who said there was no safe level of smoke and that the ban on smoking indoors should be absolute.

BBC: Wales smoking ban forced Casualty story change says