Smoking habit in parents and exposure to environmental tobacco smoke in elementary school children of Milan

Children with smoking parents are potentially exposed to Environmental Tobacco Smoke (ETS). The aims of this study were: 1) to assess ETS exposure in Milan schoolchildren, by measuring urinary cotinine (COT-U), 2) to compare the parents' perception of children ETS exposure, with the actual ETS exposure measured by COT-U, 3) to explore the factors influencing COT-U, including smoking bans at home, the season, and children characteristics.One-hundred school children (7-11 years) and their parents were recruited for the study in Spring 2018 (n = 81) and in Winter 2019 (n = 94), 75 children participated to both campaigns, for a sum of 175 observations. A questionnaire was submitted to parents to collect information about smoking habits in the house. COT-U was measured by LC-MS/MS in spot urine sample collected in the morning from children.Detectable COT-U levels were found in 42% and 57% of children, in spring and winter, in contrast with 17% and 13% of parents acknowledging ETS exposure. Children living with smokers or e-cigarette users (vapers) (30% of the participants) had higher COT-U levels than children not living with smokers or vapers (median 0.67, 0.46, and0.1 μg/L in spring, and 0.98, 0.85, and 0.11 μg/L in winter, respectively). Increasingly higher COT-U levels were observed in children living in homes where smoking was completely banned, allowed in the external parts of the home, or allowed in some rooms. The multiple regression analysis confirmed the positive significant effect of living with smokers, a partial smoking ban and absence of smoking ban at home, the winter season, and BMI as determinants of COT-U.ETS exposure resulted in measurable urinary cotinine in children. Smoking parents underestimate exposure to ETS of their children. Living with smokers is a determinant of COT-U, only slightly mitigated by adopting partial smoking ban