Environment and Hazard -5
The ‘Home Environment’ plays an important role in many issues affecting child health across the globe. Children in general may be vulnerable and become exposed to various other household hazards such as exposures to known harmful building materials, chemicals, radon, drinking water and well-water and nitrogen dioxide.
Poor housing conditions and poor ventilation together with household air pollution may also increase the risks of child hood diseases. Indoor exposure to environmental tobacco smoke (ETS) may also be hazardous and contribute to health consequences like asthma in those children that are affected.
Full exposure Pathway
Exposures to tobacco smoking may occur at any level along the entire stages of human development and these may include preconception (maternal and paternal smoking), pregnancy (maternal smoking and passive smoking), infancy (passive smoking), childhood (passive and active smoking) and young and adulthood (active and passive smoking). 1
The key internal exposure pathways and their possible routes for exposure to tobacco smoking that may lead to asthma include;

In utero exposure 2 – mainly concerns the maternal exposure to environmental tobacco smoke(ETS) associated with pregnancy via active or passive smoking.

Route: Trans placental
Mothers who are pregnant and are either active smokers or passive smokers run a risk of their developing foetus being exposed to the chemical toxicants of tobacco smoke transmitted via the placenta.2 The tobacco smoke constituents are initially inhaled through the respiratory airways to the smaller airways in the lungs (bronchioles) and then absorbed through the tiny gas-exchanging airway sacs (alveoli) and into the maternal blood circulation.

Indoor air exposure – particularly ‘second hand smoke’, where the children at household level are frequently getting exposed if their family members are smokers. Studies have showed that children are (the two reasons highlighted). 3

Route: Inhalation

Active smoking – refers to the active smokers who inhale the undiluted smoke directly into their lungs from the end of cigarette which is called mainstream smoke (MS). 4 Theconstituents ofmainstream smoke are believed to contain higher in doses of tobacco chemicals compared to passive smoking.

Second Hand Smoking or Passive smoking- refers to the non-active smokers who mostly inhale what is called second-hand smoke (SHS) which is a mixture of side-stream smoke(SS) comprised of both the smoke from the glowing cigarette and the exhaled air (mainstream smoke).4 Thus, the side-stream smoke is diluted because it contains both the exhaled mainstream smoke and air and may be less in concentration of the tobacco chemical constituents.4

Third-hand smoke – refers to the surface-deposited tobacco smoke chemical components which may be left in indoor environments for periods that allow change to their compositions and render them harmful to humans especially infants and toddlers who commonly practice hand-mouth on contaminated surfaces.5

Asthma
Asthma can be defined as an inflammatory airway disease involving inflammation and impairment of airway due to a complex interaction of immune cells and nonimmune environmental factors that trigger asthma such as tobacco smoking and second hand smoke. 6
Scope and nature of problem
Asthma is a very common chronic disease affecting children and is believed to affect almost 300 million people world-wide.7Evidence has shown that the prevalence of asthma has been on the rise in the last 50 years (Ref) with increasing trends noted in the industrialised and developed regions. The increase in the global burden of asthma disease ensures that important environmental factors that contribute to asthma are clearly identified for improved intervention and prevention strategies.
Risk factors
The risk factors for asthma that are commonly known include allergies, positive family history of asthma, cock-roach allergen, environmental tobacco smoke exposure(ETS), and prenatal smoking. 8 The diagram shown below in figure 1 summarises the early life risk factors for persistent asthma 9. It shows the different pathways in which environmental exposures and genetic predispositions lead to asthma. As illustrated, environmental exposures to tobacco smoke may affect a foetus in prenatal and later postnatal through impairment and inflammation of the lung resulting in asthma.
Figure 1 Showing how environmental exposures and genetic predispositions may contribute to asthma in different pathways in early life.
          Prenatal exposures                                               Postnatal exposures

Viral URTI            spread             Severe LRTI

Repeated episodes

Primary atopic            Allergen               Persistent
Sensitization               exposure             inflammation↓
Genetic Predispositions                                            Genetic Predispositions

Disease association and hazard
Studies in the past and recent have looked at the causal relationship between ETS or second hand smoke and asthma disease and have identified that ETS has been a significant indoor air hazard with the potential to causing serious health consequences such as asthma. Goodwin
According to the Global Youth Tobacco Survey carried out by World Health Organization in 2007 (WHO), about 44% of all the children living in the world were exposed to environmental Tobacco smoke at household level. 10
An updated meta-analysis study from Surgeon General’s Report (SGR) of the United States (DHHS 2006), a causal relationship between SHS and childhood induction of asthma could not be drawn to conclusion due to insufficient evidence from smaller number of studies. 11 However, a similar systematic review and meta-analysis study that examined prenatal and passive smoke exposure and asthma incidence at the UK Centre for Tobacco Control studies at University of Nottingham (2011) found that the incidence of wheeze and asthma in children and young people increased by 20% when exposed to passive smoking.12
Long term implications
The health implications of tobacco smoking are well recognized across the globe. The exposure to environmental tobacco smoke (ETS) happens across the entire life span of an individual and therefore long term implications are inevitable. Persistent asthma can be a long-term implication which adds to the global burden of asthma disease. Identifying the risk factors and aiming for primary prevention through life style changes such as avoiding maternal smoking during pregnancy could help prevent asthma. Environmental modifications and lifestyle changes may help reduce risks for asthma.
The use of international health guidelines such as the WHO Convention Framework for Tobacco Control (FCTC) 13 may provide benchmarks for health professionals and policy makers to implement strategies and interventions.
Reference

Breton CV, Byun HM, Wenton M, Pan F, Yang A, Gilliland FD. Prenatal tobacco smoke exposure affects global and gene-specific DNA methylaton. Am J Respir Crit care Med 2009; 180:462-7
Sly P, Flack F. Susceptibility of children to environmental pollutants. Ann NY Acad Sci 2008; 1140:163-83
Tung KY, Wu KY, Tsai CH, Su MW, Chen CH, Lin MH, et al. Association of time-location patterns with urinary cotinine among asthmatic children under household environmental tobacco smoke exposure. Environmental research. 2013; 124:7-12
US Department of Health and Human Services. The Health Consequences of Involuntary Smoking. A Report of the Surgeon General. Washington DC: US Department of Health and Human Services, Public Health Service, Office on Smoking and Health;1986. DHHS Publication No, (CDC) 87-8398
Matt GE,Quintana PJ,Destaillats H, et al.Thirdhand tobacco smoke:emerging evidence and arguments for a multidisciplinary research agenda. Environ Health Perspect 2011; 119:1218-26
Stapleton M, Howard-Thompson A, George C, Hoover RM, Self TH. Smoking and asthma. Journal of the American Board of Family Medicine: JABFM. 2011;24(3):313-22.
The Global Asthma Report 2011.Paris, France.The International Union Against Tuberculosis and Lung Disease.;2011.
Goodwin RD, Cowles RA. Household smoking and childhood asthma in the United States: a state-level analysis. The Journal of asthma: official journal of the Association for the Care of Asthma. 2008;45(7):607-10.
Guilbert TW, Singh AM,Danov Z, et al. Decreased lung function after preschool wheezing rhinovirus illnesses in children at risk to develop asthma. J Allergy Clin Immunol 2011; 128:532-8. e10.
WHO, 2007. Only 100% smoke-free environments adequately protect from dangers of second-hand smoke. New WHO policy recommendations point to extensive evidence. World Health Organization, Geneva, Switzerland.

U.S. DHHS. 2006. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health.

Burke H, Leonardi-Bee J, Hashim A, Pine-Abata H, Chen Y, Cook DG, et al. Prenatal and passive smoke exposure and incidence of asthma and wheeze: systematic review and meta-analysis. Pediatrics. 2012;129(4):735-44

Shibuya,K., et al., 2003.Framework Convention on Tobacco Control: development of an evidence based global public health treaty. BMJ 327,154-157