Secondhand Smoke May Lower Children's IQ

What are the affects of secondhand smoke?

A study shows that children who are exposed to tobacco smoke in the home may have lower IQs than their unexposed peers.

Despite mounting evidence about the perils of secondhand tobacco smoke exposure in children, 40% of children in the United States are routinely exposed to secondhand smoke, termed environmental tobacco smoke (ETS), in their own homes. ETS has already been definitively linked to a number of medical problems in children, including sudden infant death syndrome (SIDS), colic, middle ear disease, worsening of asthma symptoms, and other respiratory problems. Research has also begun to suggest that ETS may be neurotoxic, or damaging to the nervous system, with potential effects on the development of intellect and reasoning skills in children.

Mounting evidence of seconhand smoke dangers

A study led by doctors at the Cincinnati Children's Environmental Health Center at the Cincinnati Children's Hospital Medical Center provides new evidence that tobacco smoke may have detrimental effects on intellectual development. This study is intriguing because the researchers employed a biological marker called cotinine (a breakdown product of nicotine) to measure the levels of ETS exposure in children, rather than relying on potentially inaccurate or misleading responses to surveys to determine the level of tobacco exposure in the home. In a sample of 4,399 children aged six to 16, those with the highest levels of cotinine showed decreased performance on tests of math, reading, and visual-spatial skills that would correspond to an IQ decrease of two to five points. These decreases were observed even at very low levels of exposure to ETS.

Does secondhand smoke cause cancer?

While the study is not without limitations, including the fact that cotinine has a relatively short half-life and therefore may be less useful as a marker of long-term nicotine exposure, these findings nonetheless strongly support the argument for restriction of tobacco smoke exposure in children.

ETS also poses significant health risks for adults. Non-smokers who reside with a smoker have a 24% increase in risk for developing lung cancer when compared with non-smokers, and an increased risk of approximately 20% for development of coronary heart disease (CHD).

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Medically reviewed by Margaret Walsh, MD; American Board of Pediatrics


Yolton K, Dietrich K, Auinger P, Lanphear BP, Hornung R.
Exposure to environmental tobacco smoke and cognitive abilities among U.S. children and adolescents.
Environ Health Perspect. 2005 Jan;113(1):98-103.