Trends in hidden smoking among women in South Korea, 2008–2021: a comparison of self-reported and cotinine-verified smoking prevalence

Background Women in South Korea tend to underreport their smoking status due to negative social perceptions of smoking among women. This study aims to examine the differences between self-reported and cotinine-verified smoking prevalence among Korean men and women from 2008 through 2021 and to assess whether these differences have changed substantially over time. Methods This study was conducted using nationally representative cross-sectional data from the Korean National Health and Nutrition Examination Survey from 2008 to 2021. A total of 53 696 participants were included in the analysis. Smoking prevalence based on self-report and cotinine verification was compared by year, age, household income, educational attainment and marital status. All analyses were performed separately by sex, with a urinary cotinine cut-off of 50 ng/mL. Results The absolute differences in the prevalence of self-reported non-smoking among individuals with cotinine-verified smoking decreased from 5.41% in men and 8% in women in 2008 to 1.83% in men and 2.44% in women in 2021. The relative differences also declined, from 11.99% to 8.35% in men and from 57.38% to 36.42% in women. Among women, the decrease was particularly pronounced in those aged 19–39 years. Conclusions This study found that underreporting among women who smoke in South Korea has markedly decreased. However, approximately one-third of women who smoke continue to underreport their smoking status. Appropriate approaches are necessary for populations that tend to underreport their smoking status.