Does second-hand smoke from tobacco harm my baby?

The World Health Organization (WHO) strongly recommends that infants and children not be exposed to secondhand tobacco smoke.¹ Of the estimated 1.3 million deaths attributable to secondhand smoke in 2021, 42,000 were premature and preventable deaths in children under 15 years of age.² Exposure to secondhand smoke during pregnancy can lead to preterm birth, low birth weight, and adverse outcomes in infancy and childhood.¹ Infants and children living with smokers are at increased risk of developing respiratory disease and infections, sudden infant death syndrome (SIDS), neurodevelopmental delays, impaired cardiovascular function, and becoming overweight or obese. Children are thought to be especially susceptible to the damaging effects of secondhand smoke due to their higher rate of breathing and their ongoing development.

Preterm Birth and Birth Weight

A cross-sectional study published in 2011 (n=8,490) looked at the relationship between maternal secondhand smoke exposure during pregnancy and adverse pregnancy outcomes.³ Women who reported active smoking during pregnancy were excluded. Among mothers exposed to secondhand smoke while pregnant, 12.6% of babies had low birth weight (defined as <2.5 kg) compared to 7.7% of babies from non-exposed mothers. The average birth weight for newborns of women exposed to secondhand smoke was 3.06 kg compared to 3.2 kg for babies from unexposed women (p <0.005). The rate of preterm delivery in mothers exposed to secondhand smoke during pregnancy was 17.2% compared to 10.6% in the non-exposed group. The average gestational age for exposed women was 36.9 weeks compared to 37.7 weeks in the non-exposed group (p <0.005). 

A 2017 analysis of data from the longitudinal Healthy Start study (n=813 mother-infant pairs) had similar findings.⁴ On average, women sharing a household with smokers delivered earlier than women without secondhand smoke exposure in the home (39 vs 40 weeks, p=0.03). Infants born to women with no household smoke exposure weighed on average 3.3 kg at birth compared to 3.1 kg in the exposed group (p< 0.01). 

Sudden Infant Death Syndrome

A meta-analysis published in 2013 evaluated the relationship between SIDS and both prenatal and postnatal maternal smoking.⁵ The analysis included 35 case-control studies consisting of 21,040 cases and 5,956,030 controls across the world. Infants who died of SIDS had higher rates of secondhand smoke exposure (55% had mothers who smoked postnatally, compared to 28% for controls, p=0.002).

A 1993 case-control study of 485 cases and 1,800 controls found that both maternal and paternal smoking was associated with SIDS.⁶ Among cases, 44.3% of mothers reported smoking 1-19 cigarettes in the past two weeks compared to 24.3% of controls. Similarly, 34.3% of cases had fathers who smoked 1-19 cigarettes in the past two weeks compared to 20.6% of controls.

A 2003 case-control study including 142 cases and 2,841 controls found that postnatal parental smoking was significantly associated with SIDS.⁷ Among cases, 36% had one parent who smoked compared to 23% of controls (p=0.008), and among 31%, both parents smoked compared to 9% of controls (p<0.001). For 43% of cases, mothers smoked compared to 14% of controls, and 45% of fathers smoked compared to 28% of controls (p<0.001 for both).

Respiratory Conditions

A prospective, population-based cohort study of data collected from 1997-1998 (n=8,327 parent-infant pairs) studied the relationship between secondhand exposure and utilization of health services within the first 18 months of life.⁸ For the purposes of the study, high hospital utilization was defined as above the median number of hospitalizations within the study sample. Infants born to mothers exposed to secondhand smoke during pregnancy had a higher incidence of high hospital utilization for both respiratory illness or fever (18.7% vs 16.8%, p=0.037) and any illness (29.6% vs 26%, p<0.001). Secondhand smoke exposure postnatally was also related to hospitalization rates. Infants exposed to secondhand smoke at home had higher hospital utilization than non-exposed infants for respiratory illness or fever (19.5% vs 17.1%, p=0.009) and any illness (30.6% vs 27%, p<0.001). There was a dose-dependent gradient between the total number of smokers at home and more hospitalizations. Among infants hospitalized for respiratory illness or fever, 17.1% had no smokers at home, 18.9% had one smoker at home, and 21.7% had two or more smokers at home (p=0.01). Similarly, among infants hospitalized for any illness, 27.0% had no smokers at home, 29.4% had one smoker at home, and 34.6% had two or more smokers at home (p<0.001). 

A case-control study in 1999 looked specifically into the relationship between secondhand smoke and ear infections in children 3-7 years of age.⁹ In this study, 166 children who required tympanostomy tubes for otitis media with effusion or recurrent otitis media were compared to an age-matched control group. Children with tympanostomy tubes had more exposure to secondhand smoke (average of 19.6 cigarettes per day compared to 14.4 cigarettes in the control group, p<0.004). 

A 2024 meta-analysis of longitudinal studies examined the effect of postnatal environmental tobacco smoke on the risk of new onset asthma and recurrent wheezing.¹⁰ Analysis of 13 studies with a median of eight years of follow-up, postnatal exposure to tobacco smoke increased the incidence of new-onset asthma by 9 per 1,000 person-years. Analysis of 10 studies with a median of 2 years of follow-up found that recurrent wheezing increased by 24 per 1,000 person-years.

Neurodevelopment

A prospective study from 2011 (n=414 nonsmoking mother-infant pairs) evaluated the effects of prenatal and postnatal secondhand smoke exposure on neurodevelopment in babies at six months old.¹¹ Infant development was assessed using the Bayley Scales of Infant Development (standardized mean score of 100 with a standard deviation of 15, scores <85 indicate developmental delay). The study found that for the average Mental Developmental Index (MDI) score was 98.2 in the group without prenatal smoke exposure (n=151), compared to 95.67 in the prenatally exposed group (n=263). The rate of moderate developmental delay was 10.6% in the prenatal unexposed group compared to 19.0% in the prenatal exposed cohort (p<0.05). The average MDI score was 96.52 for the postnatal unexposed group (n=201) compared to 98.03 in the unexposed group (n=126).

Cardiovascular Health

The American Heart Association cautions that children are especially vulnerable to deleterious health effects associated with secondhand smoke exposure, including arterial function and structure, impaired cardiac autonomic function, and changes in heart rate variability.¹²

A 2007 longitudinal study found that secondhand smoke exposure in children was associated with arterial damage. Secondhand smoke exposure was assessed using serum cotinine concentration, a compound found in secondhand smoke, measured annually in 327 children from ages 8-11. Higher cotinine concentrations were associated with reduced peak flow-mediated dilation response (mean 9.10% vs 7.73%, p=0.03).¹³

Overweight and Obesity

A 2011 study of six-year-old children (n=1,954) looked at the relationship between being overweight and their mother smoking during pregnancy or childhood exposure to secondhand smoke.¹⁴ Children of mothers who smoked while pregnant were more likely to be overweight (13.7% vs 8.0%, OR 1.83, 95% CI [1.27-2.63]). Among children who weren’t exposed to secondhand smoke during their childhood, the rate of being overweight was 5.2% compared to 11.2% for those who were exposed to secondhand smoke in the year after birth (OR 2.32, 95% CI [1.18-4.57]) and 15.6% for those who were exposed within a year of the time of the study (OR 3.38, 95% CI [2.24-5.10]).

A 2014 analysis of longitudinal data collected from 1991-2007 (n=932) examined the effect of mothers smoking during pregnancy and postnatal secondhand smoke exposure on the development of obesity in children followed from birth to 12-16 years of age.¹⁵ Adolescents whose mothers smoked while pregnant were more likely to be obese (27.9% vs 21.8%, OR 1.67, 95% CI [1.10-2.56]). Adolescents with childhood secondhand smoke exposure were also more likely to be obese (20.7% vs 29.0%, OR 1.55, 95% CI [1.04-2.29]).

A 2021 analysis of a longitudinal population-based cohort study (n=632) conducted from 1989-2010 found that childhood exposure to secondhand smoke was associated with overweight/obesity later in life.¹⁶ Among children exposed to secondhand smoke from 2-4 years of age, the prevalence of overweight/obesity was 12% compared to 8% among unexposed children. Prevalence of overweight/obesity at age 20 was 20% for those exposed to secondhand smoke compared to 14% for those unexposed.

References

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2. Global Burden of Disease Study [online database]. Institute for Health Metrics and Evaluation, University of Washington; 2021.
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