To the Editor: The adverse health effects of environmental tobacco smoke (ETS) are well documented. Workplaces are increasingly smoke-free, and restrictions on smoking in restaurants, pubs and clubs are increasing. Paediatricians counsel parents to make their children’s home smoke-free and to smoke outside if they can not quit. In Australia, attention is turning to ETS exposure in cars, in the belief that the confined space may result in increased exposure, even if the windows are wound down. However, few, if any, objective data on the health effects of ETS exposure in cars have been published.

We report here the risks of current wheeze at the age of 14 years in children exposed to ETS in their parents’ car. Questionnaire data were available from parents of 1427 children taking part in the 14-year assessment of a longitudinal birth cohort in Perth. Characteristics of the cohort have been described elsewhere.1 Information about current wheeze (defined as the occurrence of wheeze in the previous 12 months) and asthma risk factors, including ETS exposure in the house and car, was obtained. Standard spirometry, methacholine challenge and skin prick tests to local aeroallergens were performed in 1400, 1334 and 1308 children, respectively. Current wheeze was reported in 191 children (14.0%) at the age of 14 years, compared with 537 (38.2%) when they were seen at 6 years of age. Persistent wheeze, at both 6 and 14 years of age, was reported in 145 children (10.2%).

ETS exposure in the parents’ car was common. The 14.6% of children who were exposed at 14 years had increased risk of both current wheeze (odds ratio [OR], 1.55; 95% CI, 1.02–2.35; P = 0.038) and persistent wheeze (OR, 2.14; 95% CI, 1.34–3.42; P = 0.001). These risks were higher than those for ETS in the home: for the 8.9% of children exposed in the home, the OR for current wheeze was 1.33 (95% CI, 0.80–2.22; P = 0.27) and the OR for persistent wheeze was 1.98 (95% CI, 1.12–3.50; P = 0.016). Those with current wheeze and ETS exposure in the car had increased methacholine responsiveness: PC20 (provocative concentration required to produce a 20% fall in forced expiratory volume in 1 second) was 5.9 mg/mL in children with ETS exposure compared with 15.2 mg/mL in those not exposed (P = 0.004). These effects were independent of sex and atopic status.

These data provide evidence that the community needs to be educated about the adverse health consequences of ETS exposure in cars and suggest that health care professionals should include such education in counselling sessions for families of children with asthma. Teenagers can escape ETS exposure in the home, either by removing themselves or by their parents smoking outside. However, children of this age and younger have no choice but to travel with their parents in the car, especially given the phenomenon of “mum’s taxi” transporting children to school and extracurricular activities. Smoke-free cars are important for all children.