4.7 Health effects of secondhand smoke for infants and children

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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,19 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.19 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.16

Infant health is compromised by exposure to tobacco smoke before birth, through maternal active smoking and exposure to secondhand smoke, and following birth, by exposure to parental secondhand smoke in the home. Nicotine is secreted in the breast milk of mothers who smoke, and cotinine, one of the main metabolites of nicotine, is found in the urine of breastfed infants of mothers who smoke, as well as in the urine of infants who are exposed to secondhand smoke.38 Residue from secondhand smoke is present in household dust and on surfaces, and may persist in the environment up to months following emission. This is of particular significance for young infants due to their increased likelihood of contact with floors, carpets and blankets.39

4.7.1 Infant death

Infant death is defined as the death of a child within its first year of life.20 Several of the major causes of death during infancy, including low birthweight, preterm delivery and Sudden Infant Death Syndrome, are also associated with exposure to smoking in utero and following birth. The infant mortality rate for children of smokers is 68% higher than among children of non-smokers.20

4.7.2 Sudden Infant Death Syndrome (SIDS)

SIDS is defined as the sudden, unexpected death of an infant under one year of age.20 Postnatal exposure to secondhand smoke is a cause of SIDS,19, 20 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 allergies and 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.19

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.40 The more recent California Environmental Protection Agency report has reported that the risk is three and half times greater, and has attributed about 10% of SIDS deaths in that state to secondhand smoke.19 The risk is higher for infants whose mothers smoke during pregnancy as well.20 This makes exposure to secondhand smoke a major preventable risk factor for SIDS.20 The efforts of parents to protect their children from secondhand smoke by not smoking within the home in recent years are likely to have reduced to some extent the numbers of deaths from SIDS attributable to secondhand smoke.40

4.7.3 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.20

The prevalence of asthma is also greater among children living in households with smokers, the risk increasing with the number of smokers in the home.20 The National Health and Medical Research Council (NHMRC) (1997)16 and the Californian Environmental Protection Agency (2005)19 have both concluded that secondhand smoke causes and exacerbates asthma in children. The US Surgeon General's report for 2006 remains more cautious, stating that the evidence is 'suggestive' of a causal relationship between secondhand smoke and the onset of childhood asthma.20 The NHMRC has estimated that about 8% of childhood asthma incidence in Australia is caused by secondhand smoke, with children of mothers who smoke more than 10 cigarettes daily being most severely affected.16

Children exposed to secondhand smoke may register increased allergic sensitisation,16, 19 and also be more likely to snore.41, 42 Recent research has found 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.43

4.7.4 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 croup, bronchitis, bronchiolitis and pneumonia.19, 20 Increased risk is greater in households in which the mother smokes. The effect is more pronounced in younger children (aged under two),19, 20 although there is evidence that children of school age are also affected by exposure to secondhand smoke.16

Thirteen percent of lower respiratory illnesses in children aged less than 18 months may be attributed to secondhand smoke. Children who live in a smoky household for the first year and half of their lives have a 60% higher likelihood of developing lower respiratory illness than unexposed children.16

4.7.5 Decreased lung function

The lungs continue to grow and develop throughout childhood and adolescence, peaking in young adulthood. Secondhand smoke causes decreased lung function during childhood, leading to a reduced maximum level in adulthood.20 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,19 and possibly increases the risk of developing future chronic lung disease.20

4.7.6 Middle ear disease

Middle ear disease (otitis media) occurs when bacteria, typically Streptococcus pneumoniae or Haemophilus influenzae, migrate from the nasopharyngeal region to the middle ear via the Eustachian tube and cause infection. Exposure to secondhand smoke causes middle ear disease, including acute and recurrent otitis media and chronic middle ear effusion ('glue ear'). Moreover, ear disease in children of smokers appears less likely to resolve spontaneously than among children of non-smokers.20 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.44

4.7.7 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.45

4.7.8 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.19, 20, 46

4.7.9 Childhood cancers

There is a growing body of evidence suggesting an association between prenatal and postnatal exposure to secondhand smoke and brain tumours, lymphomas, and acute lymphocytic leukaemia in children, but more research is needed.19, 20, 47

4.7.10 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.48, 49 There is also evidence that children exposed to secondhand smoke have a different metabolic response to drugs administered during surgery.50