Secondhand smoke (SHS), also known as environmental tobacco smoke, is a mixture of the side stream smoke released by a smoldering cigarette, pipe, hookah/waterpipe, or cigar, and the mainstream smoke exhaled by a smoker. SHS is a complex mixture containing thousands of chemicals, including formaldehyde, cyanide, carbon monoxide, ammonia, and nicotine. More than 250 of the chemicals in tobacco smoke are known to be harmful, and at least 69 are known to cause cancer. Secondhand aerosol (commonly incorrectly called “vapor” by the public) is a mixture of chemicals in the aerosol exhaled by e-cigarette users. Many of the chemicals identified in SHS are present in secondhand aerosol, but many are at much lower concentrations. However, this aerosol may contain nanoparticles and other constituents not found in tobacco smoke, partially a result of various flavorings in e-cigarettes.
Conclusive scientific evidence documents that SHS causes premature death and disease in children and adults who do not smoke. Exposure to SHS by adults has immediate adverse effects on the cardiovascular system, and long-term exposure to SHS causes coronary heart disease and lung cancer. Children exposed to SHS are at increased risk for sudden infant death syndrome, acute respiratory infections, middle ear disease, more severe asthma, respiratory symptoms, and slowed lung growth. At present there is little known about the impact of secondhand aerosol from e-cigarettes. However, some preliminary studies have found the presence of nicotine and some other constituents in the aerosol. Current and future research will reveal the impact of second-hand aerosol from e-cigarettes as well as the direct effects on the user.
There is no risk-free level of exposure to SHS, and only eliminating smoking in indoor spaces fully protects nonsmokers from exposure to SHS. Over the years, the focus of clean indoor air policies has shifted from partial restrictions on smoking to complete bans in a variety of environments, such as workplaces, bars, restaurants, and homes.