concept, and researchers are still studying its possible dangers. Third-hand smoking can be a serious concern, as it affects other people's health. In a house, the tobacco residue of the smoke can build up on surfaces over time. Unfortunately, excess smoke can not be removed just by airing out rooms and opening windows. Scientists have reported that third-hand smoke may cause up to 60 percent of the harm caused by regular exposure to smoke. Second-hand smoking vs third-hand smoking Second-hand smoking (SHS) is a combination of sidestream smoke (i.e., smoke emitted from the burning cigarette, pipe, or cigar) and the mainstream smoke exhaled from the lungs of smokers. It contains more than 4,000 chemicals, many of which are known to affect health. These may include ammonia, acrolein, carbon monoxide, hydrogen cyanide, nicotine, nitrogen oxides, arsenic, and sulfur dioxide, many of which contain irritants and toxicants to the eye and respiratory tract. Third-hand smoking (THS) consists of residual tobacco smoke pollutants that remain on surfaces and in dust after tobacco has been smoked, are re-emitted into the gas phase, or react with oxidants and other compounds in the environment to yield secondary pollutants. Chemicals of tobacco smoking include nicotine, 3-ethenylpyridine (3-EP), phenol, cresols, naphthalene, formaldehyde, and tobacco-specific nitrosamines (including some not found in freshly-emitted tobacco smoke). References Tobacco