||It has been suggested that this article be merged with Passive smoking. (Discuss) Proposed since November 2012.|
The term "third-hand smoke" is a neologism coined by a research team from the Dana–Farber/Harvard Cancer Center. The 'third-hand' component of the term is a reference to the remnants on surfaces after "second-hand smoke" has cleared out. The term "first-hand smoke" refers to what is inhaled into the smoker's own lungs, while "second-hand smoke" is what is a mixture of exhaled smoke and other substances leaving the smoldering end of the cigarette and enters the atmosphere and can be inhaled by others; third-hand smoke, by that token, is contamination on the surfaces of objects that remains after the second-hand smoke has cleared.
Potential harm 
Although "second-hand smoke" dissipates from a room or confined space after a short period of time, nicotine and other components of the smoke tend to coat a space's surfaces and continue to emit toxins. A 2010 study published in the Proceedings of the National Academy of Sciences journal found that the residue of the nicotine coating interior car or room surfaces can react with nitrous acid present in the air to create tobacco-specific nitrosamines, carcinogens found in tobacco products. This was demonstrated by spraying what was termed a "high but reasonable" level of nitrous acid (about 4-12 times the levels typically found in homes) onto cellulose substrates used to wipe the interior of a vehicle that had been heavily smoked in over time. Similar results were found when cellulose substrates were kept (without wiping) in the same vehicle for three days when smoking occurred. Ensuring ventilation while a cigarette is smoked does not eliminate the deposition of third-hand smoke in an enclosed space, according to the study's authors. The study found that eleven carcinogenic compounds could be found in third-hand smoke, including the radioactive element polonium-210. Third-hand smoke is thought to potentially cause the greatest harm to infants and young children, because younger children are more likely to crawl on the floor and eat from their hands without washing them first, ingesting the toxins into their systems. Currently, however, the actual magnitude of risk, if any, remains unknown.
Public awareness and implications 
Third-hand smoke is a relatively newly-discovered concept, and public awareness of it is lower than that of second-hand smoke. While a survey of 1,500 United States residents conducted over the telephone in 2005 found that the vast majority of both smokers and non-smokers recognised the dangers of passive smoking to non-smokers, 65 percent of non-smokers and 43 percent of smokers recognised the potential risks of third-hand smoke. It should be noted that the participants in the survey were simply asked 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”; there was no reference to the term or specific concept of thirdhand smoke.
Several United States courts have recognised the theoretical dangers of third-hand smoke, especially in situations where infants, small children and gestating fetuses are involved. In one case, McCormick v. Moran, heard in the New York City Civil Court in 1999, the defendant refused to refund a security deposit for an apartment on the basis that significant cleaning was required to remove tobacco smoke residue ('third-hand smoke'). The court rejected the plaintiff's argument that the extensive cleaning was not necessary and found that the residue created "an offensive odor and a potential health risk that may arise to others who may use the premises." In another example, the anti-smoking group Action on Smoking and Health demanded that a smoking coworker of a pregnant employee of Lamar University or the employee herself be transferred to another office within the University after two doctors confirmed a diagnosis of tobacco smoke allergy, and advised the employee that the third-hand smoke was putatively causing health problems for her and her unborn baby and that she should not work in the same space as the coworker.
In October 2011, it was reported that Christus St. Frances Cabrini Hospital in Alexandria, Louisiana would ban third hand smoke beginning in July 2012, and that employees whose clothing smelled like smoke would not be allowed to work. The ban was ostensibly enacted because third hand smoke allegedly poses a special danger for the developing brains of infants and small children.
- Ballantyne C (January 6, 2009). "What is third-hand smoke?". Scientific American.
- Sleiman M, Gundel LA, Pankow JF, Jacob P, Singer BC, Destaillats H (April 2010). "Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards". Proc. Natl. Acad. Sci. U.S.A. 107 (15): 6576–81. doi:10.1073/pnas.0912820107. PMC 2872399. PMID 20142504.
- "Third-hand smoke a danger to babies, toddlers". MSNBC.
- Caryn Rabin, R (January 2, 2009). "A New Cigarette Hazard — 'Third-Hand Smoke'". The New York Times.
- Matt GE, Quintana PJ, Destaillats H, et al. (September 2011). "Thirdhand tobacco smoke: emerging evidence and arguments for a multidisciplinary research agenda". Environ. Health Perspect. 119 (9): 1218–26. doi:10.1289/ehp.1103500. PMC 3230406. PMID 21628107.
- Four new dangers to non-smokers - Action on Smoking and Health. Retrieved December 6, 2010.
- McCormick v. Moran, 182 Misc. 2d 568 - NY: City Court 1999. Retrieved December 6, 2010.
- Legal Actions For Discriminating Against Pregnant Disabled Employee - John F. Banzhaf III. Retrieved December 6, 2010.
- Louisiana Hospital to Ban Odor of Smoke on Workers' Clothes, Fox News, October 3, 2011