Environmental tobacco smoke (ETS) contains a mixture of toxic chemicals, including known human carcinogens. The U.S. Surgeon General has concluded that ETS causes a range of adverse health outcomes in adults, ranging from nasal irritation to increased risk of coronary heart disease to lung cancer. In children, the Surgeon General has concluded that ETS causes lower respiratory illnesses, adverse effects on lung function, onset of wheezing, asthma, middle ear disease, and Sudden Infant Death Syndrome (HHS, 2006). Household ETS exposure is an important issue because many people, especially young children, spend much time inside their homes. Infants and younger children are more susceptible and vulnerable to the effects of ETS than are older children because they are still developing physically, have higher breathing rates than adults, and have little control over their indoor environments (HHS, 2006; U.S. EPA, 2018).
Exposure to ETS leaves traces of specific chemicals in people's serum, urine, saliva, and hair. Cotinine is a chemical that forms inside the body following exposure to nicotine, an ingredient in all tobacco products and a component of ETS. Following nicotine exposures, cotinine can usually be detected in serum for at least 1 or 2 days (Pirkle et al., 1996). Active smokers almost always have serum cotinine levels higher than 10 nanograms per milliliter (ng/mL), while non-smokers exposed to typical levels of ETS have serum concentrations less than 1 ng/mL. Following heavy exposure to ETS, non-smokers can have serum cotinine levels between 1 and 10 ng/mL (CDC, 2009, 2015).
The purpose of this indicator is to track exposure to ETS, or secondhand smoke, among the non-smoking U.S. population. Cotinine is considered the best biomarker for tracking exposure among non-smokers to ETS. Accordingly, this indicator reflects serum cotinine concentrations in ng/mL among non-smokers for a representative sample of the U.S. population, age 3 years and older, as measured in the 1988-1994, 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, 2011-2012, 2013-2014, and 2015-2016 National Health and Nutrition Examination Survey (NHANES). NHANES is a series of surveys conducted by the Centers for Disease Control and Prevention's (CDC's) National Center for Health Statistics, designed to collect data on the health and nutritional status of the civilian, non-institutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. Serum cotinine also was monitored in individuals age 4 years and older as part of NHANES III, between 1988 and 1994. CDC's National Center for Environmental Health conducted the laboratory analyses for the biomonitoring samples. Beginning in 1999, NHANES became a continuous and annual national survey. The continuous NHANES does not include cotinine data for children from birth to 3 years of age, the group reported to be the most vulnerable to the effects of ETS.