Secondhand Smoke: It’s Time to Clear the Air

What is Secondhand Smoke?

CDC: Secondhand smoke (SHS) is the combination of smoke from the burning end of a cigarette and the smoke breathed out by smokers.

Global Burden of Disease Study (2017)

  • Estimated that exposure to SHS was responsible for more than 1.2 million premature deaths worldwide in 2017

Estimated Worldwide Mortality Attributed to Secondhand Tobacco Smoke Exposure (2020)

  • Estimated that worldwide, for every 52 individuals who smoke, there is one associated death in a nonsmoker attributable to SHS exposure (SHS index)
  • SHS index is changing favorably overtime, from 31.3 in 1990 to 52.3 in 2016
  • Large regional variability – the SHS index in North America is 85.7

Effects on Children

Sudden Unexpected Infant Death (SUID; previously known as SIDS):

  • SUID = the unexpected death of a seemingly healthy infant while sleeping
  • 25-40% of SIDS cases are related to smoking during pregnancy
  • Another analysis found that for every 1% increase in the state-level prevalence of smoke-free homes with infants, the SIDS rates for the states decreased by 0.4%, while controlling for supine sleep position

Respiratory effects:

Middle ear disease:

  • SHS exposure is associated with increased risk of otitis media
    • Most consistently – increased risk of recurrent infections
    • Meta-analysis of children in a household with SHS exposure:
      • Increased risk of MED by OR 1.62 with maternal postnatal smoking
      • Increased risk of MED by OR of 1.37 for any household member smoking
      • Prenatal maternal smoking, in this case, showed a non-statistically significant increased risk for MED (OR, 1.11; 95% CI, 0.93-1.31)
  • SHS increases risk of sensorineural hearing loss in adolescents (directly related to level of exposure)

Other effects: 

Effects on Pregnancy

Maternal smoking during pregnancy (tobacco smoke components cross the placenta):

  • Increased risk of stillbirth and neonatal death
  • SUID (estimated 25-40% of cases associated with smoking during pregnancy)
  • Reduces birth weight by 200g on average
  • Non-chromosomal birth defects
    • Limb reduction defects, clubfoot, craniosynostosis, orofacial clefts, eye anomalies, GI defects (gastroschisis and abdominal hernias), cardiovascular malformations, and cryptorchidism
  • Possible cognitive deficits and structural brain changes – effects were small, long-term effect unknown

Maternal exposure to SHS during pregnancy – VERY SIMILAR OUTCOMES IN INFANTS!

  • Reduced birth weight
    • Extent of reduction is less than that for active maternal smoking
  • Higher rate of stillbirth
  • Congenital malformations
    • 1.2-2.6x more likely compared to children of non-exposed mothers
  • Possible executive function problems

Secondhand Marijuana Smoke

“One minute of marijuana secondhand smoke impairs vascular endothelial function” –Wang et al (2016)

Smoking marijuana (MJ) during pregnancy: 

  • THC crosses the placenta – concentrations in the fetus are about ⅓ of the levels found in mom
  • University of Washington survey of 90,000 pregnant women in the US found that about 1 in 10 pregnant used MJ in the past year, 3.9% used it in the past month
  • Effects of prenatal marijuana on the infant:
    • Increased risk of stillbirth (2x risk) or neonatal death
    • SGA or low birth weight
    • Brain functioning – decreased ability for regulation and habituation; increased irritability, startle response and tremors
  • Effects of prenatal marijuana on growing children:
    • Associations with inattention, impulsivity, memory deficits, and under achievement in reading/spelling at age 10 (no impact on actual IQ)
    • Deficits in some executive functioning in adolescents, including problem-solving skills

Effects on children: 

  • Cannabinoid metabolites are frequently identified in the bodily fluids in those exposed to secondhand smoke in the household, and they can experience psychoactive effects
  • Posis et al (2019) looked at 5 smoking-related childhood health outcomes: 1) ED visits for coughing/difficulty breathing, 2) diagnosis of ear infection, 3) bronchitis/bronchiolitis, 4) asthma, and 5) eczema
    • Odds of reporting a greater number of these adverse health outcomes in the last year was 1.8x higher for children exposed to indoor cannabis smoking vs children without exposure (p = 0.10) – not statistically significant 
    • However, “the magnitude of the…association between indoor cannabis smoking and adverse health outcomes warrants more studies.”
  • Children with parents who use marijuana are more likely to use MJ and alcohol themselves
    • Particularly if marijuana use occurs during their adolescent years

What can we do about SHS?


  • Talk to parents about SHS during “teachable moments”
    • Pregnancy
    • Birth of a child
    • Early childhood (child imitates smoking behaviors)
    • Acute illness of child related to smoking (otitis media, asthma exacerbation)
    • One study argues that we should emphasize the impact of quitting smoking on the child (as opposed to impacts on parents themselves).
      • For example, the most preferred messages were “Quitting smoking will improve your child’s health by preventing respiratory illnesses like coughs, colds, and wheezing” and “Quitting smoking will decrease your child’s risk of getting lung cancer and other cancers by keeping them away from secondhand smoke.”
  • AAP recommends assessing smoking status of household members at each well-child AND acute-care visit
    • Provide guidance in cessation or referral to cessation programs
  • Intermediate steps to reduce exposure (if parent CANNOT quit):
    • Smoke outside, away from children and other non-smokers
    • Don’t smoke inside your car, even with the windows open 
  • Do your patients have pets? SHS may be making them sick, too!

Blog post based on Med-Peds Forum talk by Lindsey Mahoney, PGY4

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