二手烟（也称环境烟草烟雾、非自愿吸烟或被动吸烟）是一种由4000多种化学物质组成的复杂混合物，其中包括至少69种已知致癌物和更多种其它有害健康的物质。《烟草控制框架公约》这一国际烟草控制条约指出：“科学证据已明确证实接触烟草烟雾会引起死亡、疾病和功能丧失。”世界卫生组织指出，二手烟是一种人类致癌物，它不存在“安全”暴露水平1。
全世界的卫生和科学权威机构一致认为，二手烟对人类健康构成了严重威胁，必须采取有效行动降低人们对二手烟的暴露。他们的结论包括：
接触二手烟的健康风险的科学证据明确、令人信服，数量众多。美国卫生总监2006年6月发表了关于二手烟的权威科学报告《被动接触烟草烟雾的健康后果》，该报告得出以下结论：
《公约》的一项指导原则要求各国政府“保护所有人免于接触烟草烟雾”，而不仅仅是儿童或孕妇等特定的人群。保护应覆盖“室内工作场所、公共交通工具、室内公共场所，以及...其它公共场所。”
世界各地的卫生权威机构一致认为，消除二手烟暴露的唯一有效方法是制定全面的无烟法律（禁烟），包括所有的室内工作场所和公共场所，推荐该政策的卫生权威机构包括：
近年来，越来越多的国家、省、州、或地区通过了全面的无烟法律。这些国家和地区包括：百慕大、不丹、英格兰（2007年7月1日生效）、法国（2008年生效）、爱尔兰、意大利、立陶宛、新西兰、北爱尔兰、挪威、苏格兰、瑞典和乌拉圭。
全面的无烟法律禁止在以下区域吸烟：
除无烟法律外，世界卫生组织还推荐采取以下行动，减少二手烟暴露：
为了减少在家中二手烟的暴露，许多儿童在家中暴露于二手烟，世界卫生组织推荐各国政府开展针对家庭决策者的教育宣传，强调二手烟对儿童和其他非吸烟者的不良影响7。
烟草行业试图与餐饮招待行业结盟，建立和资助了一些声称代表酒吧、酒店和餐馆业主的“代表机构”。这些机构带头反对无烟法律，认为餐饮场所和其它人们聚会场所的生意将因为禁烟遭受巨大财务损失。但是世界各地的研究表明这些说法没有根据。
虽然科学证据众多，世界上五大烟草公司中的四家仍然公开坚持二手烟对非吸烟者没有危害。但是，烟草公司私下里认为，正在出现的公众对二手烟的担忧和意识是对他们业务的主要威胁。烟草公司使用了多种手段对抗无烟政策，其中包括：
对科学提出挑战
推广“迁就通融”和“尊重选择”项目
所以也许不奇怪，《美国医学会杂志》对二手烟文章的分析发现，“唯一与得出被动吸烟没有危害的结论相关的因素是作者是否隶属于烟草行业。”16
World Health Organization Tobacco Free Initiative:
www.who.int/tobacco/communications/events/wntd/2007/smoke_free/en/index....
2006 U.S. Surgeon General’s Report: The Health Consequences of Involuntary Exposure to Secondhand Smoke:
www.cdc.gov/tobacco/data_statistics/sgr/sgr_2006/index.htm
2005 California Environmental Protection Agency Report on secondhand smoke
http://repositories.cdlib.org/tc/surveys/CALEPA2005/
2003 World Bank report on Smoke Free Workplaces
http://web.worldbank.org/WBSITE/EXTERNAL/TOPICS/EXTHEALTHNUTRITIONANDPOP...
ON/EXTPHAAG/0,,contentMDK:20796948~menuPK:1314827~pagePK:64229817~piPK:64229743~the
SitePK:672263,00.html
2002 International Agency for Research on Cancer Monograph on Tobacco Smoke and Involuntary Smoking
http://monographs.iarc.fr/ENG/Monographs/vol83/volume83.pdf
TobaccoScam, a project to curtail the tobacco industry’s manipulation of the hospitality industry:
www.tobaccoscam.ucsf.edu
U.S. National Toxicology Program – 10th Report on Carcinogens
http://ehp.niehs.nih.gov/roc/tenth/profiles/s176toba.pdf
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