The smoke that comes from a lit cigarette contains many different poisonous chemicals. In the past, scientists did not think that these chemicals could harm non - smoker’s health. Recently, though scientists changed their opinion after they studied a large group of no – smokers, they discovered that even non - smokers had unhealthy amounts of these toxic chemicals in their bodies. As a matter of fact, almost all of us breathe tobacco smoke at times, whether we realize it or not. For example, we cannot avoid smoke in restaurants, hotels and other public places. Even though many public places have “non - smoking is permitted”, It is even harder for children to avoid second - hand smoke. In the United States, nine million children under the age of five live in homes with at least one smoker. Research shows that these children are sick more often than those who live in homes where non – smokers live. The damaging effects of second - hand smoke on children also continue are they grow up. The children of smokers are more than twice as likely to develop lung cancer when they are adults as the children of non - smokers. The risk is even higher among children who live in homes where both parents smoke.