The Relationship Between Exposure to Incense Smoke, and The Incidence of Asthma, or Lung Cancer: A Systematic Review

Abstract

Background: Incense burning is common practice in many parts of Asia, especially in Chinese, Indian and Arabic communities. While indoor air pollution is known to be harmful to one’s respiratory health, the effects of incense smoke have not been studied extensively. Incense smoke can contribute to indoor pollution and hence has potential to cause Asthma and Lung Cancer. Aims/Objectives: To analyse the relationship between exposure to incense smoke, and the incidence of Asthma, or Lung Cancer Design: Systematic review Methods: Cohort and case control studies that analysed the relationship between incense, and Asthma or Lung Cancer with participants between ages of 2 to 84 were considered for inclusion. EMBASE, CINAHL, PubMed, Web of Science, Scopus, Cochrane, and ProQuest theses and dissertations were searched. Data extraction and critical appraisal was done by two independent reviewers. NOS was used to appraise articles while GRADE was used to assess for overall quality. Effect size was summarised using median odds ratio and interquartile range. Vote counting based on direction of effect and narrative summary was done. Results: Median odds ratio for Asthma and Lung Cancer studies is 1.25 (IQR 0.73), and 1.28 (IQR 0.45) respectively. Funnel plot asymmetry and Egger’s test suggests presence of publication bias (p=0.020) for Asthma studies. A symmetrical funnel plot and Egger’s test does not suggest presence of publication bias (p=0.400) for Lung Cancer studies. Both outcomes scored very low on the GRADE scale. Conclusion: Incense smoke could be a risk factor for Asthma and Lung Cancer but low quality of evidence should be considered. Implications: There is insufficient evidence to translate into practice and policy. More large, prospective studies focusing on the relationship between incense smoke, and Asthma or Lung Cancer with other unexplored variables would contribute greatly to this topic.