Almost all youth in economically disadvantaged urban areas were exposed to tobacco smoke: secondhand smoke was most prevalent among African Americans. ScienceDaily. Almost all youth living in disadvantaged urban areas were exposed to tobacco smoke: exposure to secondhand smoke was highest among African Americans. Eighty-two percent of the adolescents were identified as nonsmokers exposed to secondhand smoke because they had NNAL levels but no cotinine levels above 30 ng per mL of urine. In a previous study, Benowitz and his colleagues showed that 87% of adolescents from an economically disadvantaged population showed signs of nicotine exposure as determined by the presence of cotinine in urine samples. Thus, he and his colleagues investigated whether NNAL, compared with cotinine, is a biomarker more sensitive to secondhand smoke, increasing the likelihood of identifying adolescents who are periodically exposed to it. “Our data show a near prevalence of tobacco smoke among these economically disadvantaged youth, underscoring the need for new public health initiatives to reduce exposure to tobacco smoke,” he added. Benowitz explained that adolescent secondhand smoke is a public health problem because it increases the risk of respiratory tract infections, exacerbates asthma and is associated with an increased likelihood of active smoking. This study proposed to evaluate exposure to tobacco smoke in this population by measuring NNAL levels in urine samples. In addition, NNAL levels in the urine of nonsmokers were higher among African American nonsmokers, indicating an increased exposure to secondhand smoke. How the study was conducted and what the results were: Researchers measured cotinine and NNAL levels in urine samples from 465 adolescents treated at Zuckerberg Central Hospital Children’s Wellness Center in San Francisco. With more than 30 ng of cotinine per mL of urine as a biomarker of active smoking, previous studies have identified 12% of adolescents as active smokers. Mr. Benowitz explained that NNAL is detectable in urine much longer after tobacco exposure than cotinine, and is only present in the urine of people who are exposed to tobacco. Therefore, using the NNAL biomarker showed a higher prevalence of tobacco exposure in this population compared to cotinine.