Passive smoking is defined as the involuntary inhalation of somebody else"s tobacco smoke. Such secondhand tobacco smoke is a mixture of mainstream smoke exhaled by active smokers and sidestream smoke released from the smouldering tobacco and diluted with ambient air. Usually passive smoking occurs in a closed environment, but it can also happen in an open environment. Passive smokers inhale carcinogens, as well as other toxic components, that are present in secondhand tobacco smoke.