Parents who smoke often open a window or turn on a fan to clear the air of second-hand smoke, but experts now have identified another smoking-related threat to children’s health that isn’t as easy to get rid of: third-hand smoke.

    That’s the term being used to describe the invisible yet toxic brew of gases and particles clinging to smokers’ hair and clothing, not to mention cushions and carpeting, that lingers long after smoke has cleared from a room. The residue includes heavy metals, carcinogens and even radioactive materials that young children can get on their hands and ingest, especially if they’re crawling or playing on the floor.

    Doctors from MassGeneral Hospital for Children in Boston coined the term “third-hand smoke” to describe these chemicals in a new study that focused on the risks they pose to infants and children. The study was published in this month’s issue of the journal Pediatrics.

    “Everyone knows that second-hand smoke is bad, but they don’t know about this,” said Dr. Jonathan P. Winickoff, the lead author of the study and an assistant professor of pediatrics at Harvard Medical School.

    “When their kids are out of the house, they might smoke. Or they smoke in the car. Or they strap the kid in the car seat in the back and crack the window and smoke, and they think it’s okay because the second-hand smoke isn’t getting to their kids,” Dr. Winickoff continued. “We needed a term to describe these tobacco toxins that aren’t visible.”

    Third-hand smoke is what one smells when a smoker gets in an elevator after going outside for a cigarette, he said, or in a hotel room where people were smoking. “Your nose isn’t lying,” he said. “The stuff is so toxic that your brain is telling you: ’Get away.’”

    The study reported on attitudes toward smoking in 1,500 households across the United States. It found that the vast majority of both smokers and nonsmokers were aware that second-hand smoke is harmful to children. Some 95 percent of nonsmokers and 84 percent of smokers agreed with the statement that “inhaling smoke from a parent’s cigarette can harm the health of infants and children.”

    But far fewer of those surveyed were aware of the risks of third-hand smoke. Since the term is so new, the researchers asked people if they agreed with the statement that “breathing air in a room today where people smoked yesterday can harm the health of infants and children.” Only 65 percent of nonsmokers and 43 percent of smokers agreed with that statement, which researchers interpreted as acknowledgement of the risks of third-hand smoke.

    The belief that second-hand smoke harms children’s health was not independently associated with strict smoking bans in homes and cars, the researchers found. On the other hand, the belief that third-hand smoke was harmful greatly increased the likelihood the respondent also would enforce a strict smoking ban at home, Dr. Winickoff said.

    “That tells us we’re onto an important new health message here,” he said. “What we heard in focus group after focus group was, ‘I turn on the fan and the smoke disappears.’ It made us realize how many people think about second-hand smoke — they’re telling us they know it’s bad but they’ve figured out a way to do it.”

    The data was collected in a national random-digit-dial telephone survey done between September and November 2005. The sample was weighted by race and gender, based on census information.

    Dr. Philip Landrigan, a pediatrician who heads the Children’s Environmental Health Center at Mount Sinai School of Medicine in New York, said the phrase third-hand smoke is a brand-new term that has implications for behavior.

    “The central message here is that simply closing the kitchen door to take a smoke is not protecting the kids from the effects of that smoke,” he said. “There are carcinogens in this third-hand smoke, and they are a cancer risk for anybody of any age who comes into contact with them.”

    Among the substances in third-hand smoke are hydrogen cyanide, used in chemical weapons; butane, which is used in lighter fluid; toluene, found in paint thinners; arsenic; lead; carbon monoxide; and even polonium-210, the highly radioactive carcinogen that was used to murder former Russian spy Alexander V. Litvinenko in 2006. Eleven of the compounds are highly carcinogenic.

    吸煙的父母常常開窗或者開電扇，使室內通風，從而清除空氣中的“二手煙”，但現在專家發現了另一種由香煙導致的難以治愈的兒童健康疾病：三手煙危害。

    這個新詞匯所指的是，房間里煙味消逝很久之后，吸煙者頭發和衣物上仍攜帶著的不可見但有毒的氣體和顆粒，不限于椅墊和毛毯上的氣體和顆粒。這些包括重金屬，致癌物資甚至放射性物資在內的殘余物，沾滿了嬰幼兒的雙手甚至被他們的呼吸道吸收。當嬰幼兒在地板上爬行或者玩耍時，所受的污染尤甚。

    在研究這些化學物資對嬰幼兒的危害的過程中，波士頓嬰幼兒大眾醫院的醫生們量身度作了“三手煙”的這個詞來描述這些化學物資。研究結果發表在這個月的小兒科雜志上。

    “每個人都知道二手煙有害，但是他們并不知道‘三手煙’”，研究報告的主要作者和哈佛醫學院的助理教授，小兒科喬娜珊-維尼沃夫說。

    “當孩子們在屋外，父母們在屋外吸煙。或者父母們把孩子放在以窗子隔離的后座上，自己在車里吸煙。這些父母認為自己做的做法很好，因為孩子們無法吸到二手煙。”維尼沃夫繼續說道，“我們需要一個詞來表述這些看不見的香煙毒素。”

    當吸煙者在外吸完一支煙走進電梯或時，旁人聞到的即是三手煙。走進有人正在吞云吐霧的房間，聞到的也是三手煙。維尼沃夫介紹說。“鼻子并不會撒謊，”他說，“這些氣味非常有害，我們的大腦都在叫囂‘出去’。”

    這個研究報告的調查對象涵蓋了全美1500個吸煙家庭，發現大多數吸煙者和不吸煙者都清楚知道二手煙有害。大約95%的不吸煙者和84%的吸煙者也同意“嬰幼兒因吸入父母煙灰缸煙味而致病”的論斷。

    但是這些被調查者中，非常少的人知道三手煙的危害。這個詞語新穎，所以調查者換了種說法0問人們是否同意“待在昨天有人抽過煙的屋子里對嬰幼兒身體不好”的論斷。只有65%的不吸煙者和43%的吸煙同意此說法。調查者即以這一比例作為公眾對三手煙的認知度。

    維尼沃夫醫生說，調查者發現，屋內和車內嚴格的禁煙令與二手煙影響兒童健康這一認知密不可分。另一方面，三手煙有害這一認知，使得被調查者更有可能強化家庭內的禁煙行為。

    “這告訴我們需要宣傳一個重要的新健康信息。”他說，“我們不停的在受訪者間聽到‘我打開了電扇，煙味都被吹走了’，從這點可知，許多人都知道二手煙有害，他們告訴我們他們知道室內抽煙不好，并且找出了一個解決的辦法。”

    研究數據是在2005年9月至11月的全國隨機電話調查中收集的。樣本家庭在人口信息的基礎上，遍布了不同種族和性別。

    領導紐約塞納毛特醫學院的兒童環境衛生中心的兒科醫生，菲利普-蘭德里甘醫生說，三手煙是一個嶄新的行為學詞匯。

    “這詞所表達的重點意義是，簡單的關上廚房門吸煙并不是避免兒童遠離香煙危害的辦法，”他說，“三手煙里的致癌物資，對與吸煙者有聯系的任何人都有潛在的危險性。”

    三手煙中的物資包括用于制造化學武器的氫氰化物，輕質石油的丁烷，涂料稀釋劑中的甲苯，砷，鉛，一氧化碳，甚至還有謀殺了前蘇聯間諜亞歷山大利維尼柯的極具放射性致癌物資釙210，三手煙中11種組成物質都是高致癌物資。