4.9 Health effects of secondhand smoke for infants and children

Compared with adults, children are particularly susceptible to the effects of secondhand smoke due to their higher breathing rates per body weight, their greater lung surface area relative to adults,1 and the comparative immaturity of their lungs. Infants and children are also generally unable to control their environment, and therefore cannot take steps to avoid exposure to secondhand smoke.1 Children are most likely to be exposed to secondhand smoke in the home, and because exposure can be so widespread, even comparatively small increases in disease risk may translate into a substantial burden of disease in infancy and childhood.2

There are several possible routes by which the effects of tobacco smoke may compromise infant health. Before birth, there is potential damage to sperm from paternal active smoking,3,4 and exposure to maternal active smoking or maternal exposure to secondhand smoke during pregnancy.1,3 Following birth, infants may be exposed to parental secondhand smoke in the home,3 to thirdhand smoke in household dust and indoor surfaces,5 and to an increased bacterial load carried by a parent or carer who smokes.68 Both prenatal and postnatal exposure have been found to contribute to several health conditions.3,9 Delineating the impact of each route of exposure in the causation of disease can sometimes be difficult, particularly for rarer conditions.

Maternal smoking also has negative effects on the quality and quantity of breast milk (see Section 3.7.1). Various tobacco smoke constituents are found in the breast milk of smoking mothers, which are ingested by their child.10 However, among smoking mothers who cannot quit, breastfeeding is considered to be better and safer than bottlefeeding.11 While it is not ideal, breastfeeding by mothers who smoke has a significant protective effect for their child, particularly against respiratory and ear infections associated with secondhand smoke exposure.1114

4.9.1 Infant death

Infant death is defined as the death of a child within its first year of life.3 Exposure to smoking in utero and following birth is associated with several of the major causes of death during infancy, including low birthweight, preterm delivery and sudden infant death syndrome. Currently, the evidence is inadequate to infer that secondhand smoke is a cause of infant death by itself.3 The US Division of Vital Statistics (2006) reported that the infant mortality rate for children of mothers who smoked during pregnancy was 58% higher than among children of non-smokers.15

4.9.2 Sudden infant death syndrome (SIDS)

Sudden infant death syndrome (SIDS) is defined as the sudden, unexpected death of an infant under one year of age.3 Postnatal exposure to secondhand smoke is a cause of SIDS,1,3 probably due to a number of mechanisms. Babies exposed to secondhand smoke are more likely to have thickening and inflammation of the airways, and are more susceptible to lung infections. Secondhand smoke may also impair the body's control over respiration and heart rate, and the automatic response to start breathing again after an episode of apnoea.1,3

According to Australian estimates, infants exposed to maternal secondhand smoke after birth have nearly two and a half times the risk of dying from SIDS compared with unexposed infants.16 The more recent reviews from the US have reported that the risk is almost doubled,1,3 and the California Environmental Protection Agency report has attributed about 10% of SIDS deaths in that state to secondhand smoke.1 The Tobacco Advisory Group of the Royal College of Physicians (2010) states that the risk of SIDS is more than doubled for infants who live with smokers.17 The risk is higher for infants whose mothers smoke during pregnancy as well.3 This makes exposure to secondhand smoke a major preventable risk factor for SIDS.3 In recent years, more parents have striven to protect their children from secondhand smoke by not smoking within their homes. Their actions are likely to have reduced to some extent the numbers of deaths from SIDS attributable to secondhand smoke.16

4.9.3 Childhood asthma and other chronic respiratory symptoms

Exposure to secondhand smoke causes a range of respiratory symptoms, such as cough, phlegm production, breathlessness and wheezing in children of primary school age. These symptoms are common in childhood, and may restrict the activities of children who experience them.3

The National Health and Medical Research Council (1997)2 and the California Environmental Protection Agency (2005)1 have both concluded that secondhand smoke causes and exacerbates asthma in children. The US Surgeon General's 2006 report states that the evidence clearly shows that secondhand smoke exposure makes asthma more severe. However, it remains more cautious about secondhand smoke exposure and the onset of childhood asthma, stating that the evidence is 'suggestive' of a causal relationship.3 The prevalence of asthma is greater among children living in households with smokers, the risk increasing with the number of smokers in the home.3 In 2004–05, 11% of Australian children with asthma were living in homes where smoking took place indoors.18 It is estimated that 2% of asthma deaths in Australian children under 15 years are attributable to secondhand smoke.19

The evidence is uncertain on whether there is an association between secondhand smoke exposure and allergic sensitisation,1,3 however some studies suggest there may be a synergy between hereditary risk for allergies and secondhand smoke exposure.3,20,21 Children exposed to secondhand smoke may be more likely to snore.2224 One large study has reported that respiratory symptoms such as chronic dry cough and phlegm production may persist into adulthood among children who live with a smoker, independent of later exposure to secondhand smoke.25

4.9.4 Acute lower respiratory tract infections in infancy and early childhood

Children exposed to secondhand smoke in the home have a greater risk of contracting acute chest infections, including bronchitis, bronchiolitis and pneumonia.1,3,26 The effect is most pronounced in younger children (aged under two).1,3 Infants who live in a smoky household have a 50% higher likelihood of developing lower respiratory illness than unexposed children.26,17 Increased risk is greater in households in which the mother smokes (about 60%).3,26,17

4.9.5 Decreased lung function

The lungs continue to grow and develop throughout childhood and adolescence, peaking in young adulthood. The period up to the age of four is a particularly vulnerable time for lung growth and development, when the number of alveoli in the lung is increasing. Secondhand smoke causes decreased lung function during childhood, leading to a reduced maximum level in adulthood.3 This impairment may potentially increase vulnerability to other insults to the lungs, such as active smoking, secondhand smoke, exposure to air pollution and occupational irritants,1 and possibly increases the risk of developing future chronic lung disease.3

4.9.6 Middle ear disease

Middle ear disease (otitis media) occurs when the Eustachian tube, which connects the middle ear to the back of the throat, becomes blocked or swollen, causing fluid to build up in the middle ear. This fluid can become infected, usually by bacteria.1,27 Exposure to secondhand smoke causes middle ear disease, including acute and recurrent otitis media and chronic middle ear effusion (fluid build-up without infection, also known as 'glue ear').3 Children who live in a smoky household have a 35% increased risk for middle ear disease, and if their mother smokes they have a 46% increased risk.17 Moreover, ear disease in children of smokers appears less likely to resolve spontaneously than among children of non-smokers.3 This has important implications for child health. Episodes of glue ear in early life are associated with hearing loss and may lead to long-term problems with speech, and a range of developmental, behavioural and social consequences.28

4.9.7 Reduced sense of smell

Children exposed to secondhand smoke in the home may have impaired olfactory function, but the research in this field is limited. One study has shown that children living with a parent who smoked a packet of cigarettes a day were more likely to misidentify the aromas of vanilla, roses, mothballs and cough drops compared with a control group of children not living with a smoker.29,30

4.9.8 Longer term developmental effects

There is some evidence to suggest an association between exposure to secondhand smoke and an impact on cognition and behaviour, including higher likelihood of childhood conduct problems and learning difficulties. This is an area requiring further research.1,3,31,32

4.9.9 Childhood cancers

There is a growing body of evidence suggesting an association between parental smoking during the preconception, prenatal and postnatal periods and brain tumours, lymphomas and acute lymphocytic leukaemia in children.1,3,33,34 The 2009 review by the International Agency for Research in Cancer (IARC) concluded that children born of parents who smoke (father, mother or both, including in the preconception period and pregnancy) are at a significantly higher risk of hepatoblastoma, a rare childhood cancer of the liver.34 Possible mechanisms include damage to sperm DNA and damage to the foetal liver from carcinogens in the blood of the pregnant mother, either from active smoking or secondhand smoke.35,36 The 2009 IARC review also stated there was limited evidence to suggest that paternal smoking before pregnancy was associated with childhood leukaemia.34,4 The relationship between secondhand smoke and childhood cancers requires further research.

4.9.10 Perioperative complications

A strong association has been observed between the incidence of respiratory complications in children undergoing general anaesthesia and a history of exposure to secondhand smoke.3739 There is also evidence that children exposed to secondhand smoke have a different metabolic response to drugs administered during surgery.40

4.9.11 Other conditions in childhood

Limited research suggests an association between exposure to secondhand smoke and dental problems in children, such as tooth decay and poorer attachment of the teeth to the gum and supporting structures.1,41,42 More research is needed.

Some studies indicate an association between exposure to secondhand smoke and gastrointestinal problems in children, such as diarrhoea and gastroenteritis.4345 More research is needed.

Recent news and research

For recent news items and research on this topic, click here (Last updated April 2016  

References

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