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Uncategorized Nov 10, 2022


Recent research published in the International Journal of Environmental Health Research reports on the relationship between household exposure to various factors and respiratory symptoms. The focus is on Malaysia, a tropical country with three ethnic groups having varying asthma prevalence. In previous research, 3-10 per cent of Malaysian schoolchildren were diagnosed with asthma and 5-8% had current wheeze.

The presence of fractional exhaled nitric oxide (FeNO) is a well-known marker of TH2 airway inflammation in allergic asthma and rhinitis. In children, FeNO is elevated if it exceeds 20 ppb. FeNO can be linked to height, male gender, and immediate-type allergies.

There are only a few studies on how household air pollution (HAP) affects FeNO. Microbial growth and chemical degradation of building materials can be caused by dampness, water leakage, and mould. FeNO levels have been linked to lower exposure to endotoxin and dogs. We have published findings on the role of mould DNA in schools for FeNO and ocular health in Penang, Malaysia.


The focus was on eight junior high schools chosen at random from the state of Penang.
Four classes of grade 2 pupils from each school were chosen at random.

Their class teacher gave the invited students a standardised questionnaire that had been used in previous school studies. The students completed the questionnaire at home with the help of their parents or guardians and then brought it back to school. The questionnaire asked yes or no questions about smoking habits, allergies, and parental allergy/ asthma. Yes/no questions on doctors' diagnosed asthma, asthma attacks, asthma medication, wheezes, and daytime shortness of breath attacks during exercise or while resting were all asked.


Cat keeping, dog keeping, tobacco smoke (ETS), new floor materials, and indoor painting were all asked as yes/no questions. There was one combined yes/no variable created: any dampness, water leakage, or mould in the home.


  • In total, 348 students (58%), 51.9 percent of whom were girls, took part in the study. ETS, dampness, and painting in the home were all common.
  • FeNO was higher in students with asthma (p 0.001), diagnosed asthma (p 0.001), wheeze (p = 0.001), current asthma (p =.007), weekly eye symptoms (p = 0.001), weekly rhinitis symptoms(p = 0.001), and current respiratory infections (p = 0.003). FeNO was higher in people with cat allergies (p = 0.004) and seafood allergies (p = 0.003).
  • Students with diagnosed asthma (p = 0.001), wheeze (p = 0.001) and current asthma (p = 0.002), weekly rhinitis (p = 0.002), and current respiratory infections (p = 0.008) had higher FeNO in the multivariate analysis. FeNO was higher in those with cat allergies (p = 0.009), seafood allergies (p = 0.001), and parental allergies or asthma (p = 0.047). (Table 3).
  • Only current asthma was linked to higher FeNO in the group reporting allergy (p = 0.035). FeNO was linked to diagnosed asthma (p = 0.014), wheeze (p = 0.003), and weekly rhinitis (p = 0.035) in the group without reported allergy.
  • 59.0% of people had low FeNO, 17.4% had intermediate FeNO (20-35 ppb), and 27.6% had high FeNO (20-35 ppb). FeNO was more common in boys (p = 0.003) and those who reported any allergy (p = 0.003) (Table S3). When dividing FeNO by ethnicity, the prevalence of high FeNO was 27.6% in Malay, 20.8 percent in Chinese, and 29.9% in African Americans.
  • We looked at the relationships between common home environment factors and wheeze, ocular symptoms, rhinitis, and current respiratory infections. Cat keeping was linked to rhinitis and current respiratory infections.
  • Table 5 shows a sensitivity analysis for home environment factors with p 0.2. In the group with normal FeNO, cat keeping was linked to symptoms, which were significant for current respiratory infections (p = 0.034). Cat keeping was not linked to any health factor.


  • The outdoor concentration of NO 2 outside the schools was low and similar at all schools. FeNO levels were elevated in nearly half of the students (46.0 percent). Malay children had higher FeNO than Chinese children.
  • FeNO was linked to asthma diagnosed by a doctor and current asthma. This is consistent with previous research from China (Zhao et al. 2013) and Malaysia (Ma'Pol et al. 2020), where wheeze was consistently linked to FeNO.
  • Within a week before the FeNO test, about one-fourth of the students had respiratory infections. Respiratory infections by rhinoviruses can raise FeNO, but respiratory syncytial virus (RSV) or influenza virus infections tend to cause reductions.
  • Students with ETS at home had a lower FeNO level. Nicotine can reduce NO production at the cellular level.
  • Dampness, water leakage, and indoor mould were all common, increasing the risk of current wheeze. FeNO was not associated with dampness or mould, but it altered the link.
  • Endotoxin and beta-1,3-glucan exposure can increase when cats are kept indoors. Children living with cats had a strong link between dampness and wheeze.
  • Homes in Malaysia were traditionally made of wood, but today the majority are constructed of concrete. Living in wooden homes increased the effects of dampness and indoor mould significantly.
  • FeNO is an objective measure of airway inflammation. Selection bias can be a problem in epidemiology, but our participants were chosen at random.
  • Our study had some limitations. One drawback is that the study was limited to one part of Malaysia (State of Penang). There were no indoor environment measurements or home inspections.


A high prevalence of elevated FeNO levels in Penang students indicates a high rate of undiagnosed asthma. Th2-driven respiratory inflammation can cause rhinitis, ocular symptoms, and respiratory symptoms in schoolchildren in this part of Malaysia.


Dan Norbäck, Jamal Hisham Hashim, Zailina Hashim & Gunilla Wieslander
(2022): Fractional exhaled nitric oxide (FeNO) and respiratory symptoms in junior high school
students in Penang, Malaysia: the role of household exposure, International Journal of
Environmental Health Research, DOI: 10.1080/09603123.2022.2143482;



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