# Indoor Air Pollution Increases the Risk of Lung Cancer
## 4 Discussion  
This study provided evidence that cooking and indoor incense burning increased the risk of lung cancer, especially in females. Environmental exposure history and the measurement of air pollutants in pleural fluid can be used to accurately predict the probability of lung cancer. By combining machine learning technology with analytical science, the public can estimate their health risks of air pollution and take protective measures to prevent lung cancer. Precision preventive medicine is a new concept that guides physicians toward preventive interventions that can work best at the population and individual levels [19]. Precision preventive medicine aims to identify significant environmental risk  
Figure 5: The important environmental factors and exposure biomarkers of lung cancer are determined by (**a**) decision tree and (**b**) random forest models showing the variable importance (VIP) score. By the decision tree, the most important factor in predicting lung cancer is the concentration of naphthalene (\(\geq\)0.61 ppb) in pleural fluid, followed by the distance between the residence and the main street and habitual cooking at home. By random forest, the most important factor for predicting lung cancer is habitual cooking at home, followed by the concentrations of ethylbenzene, o-xylene, naphthalene in pleural fluid, and then habitual indoor incense burning. factors for interventions in the entire community and provide accurate predictive models to identify high-risk individuals in need of primary prevention [20]. By using machine learning techniques, this study took into account individual differences in lifestyle, environmental exposure, and biomarkers that have complex interactions and provided a personalized probabilistic estimate of the lung cancer risk caused by air pollution. This novel method may contribute to the development of precision preventive medicine in environmental health. This study showed that naphthalene was an important exposure biomarker of lung adenocarcinoma in females. There is no direct evidence in humans that naphthalene causes cancer. However, cancer from naphthalene exposure has been seen in animal studies. Some female mice that breathed naphthalene vapors daily for a lifetime developed lung tumors [21]. We recommend more epidemiological studies to clarify the association between naphthalene and lung adenocarcinoma. Although blood and urine samples are often used as tools for biological monitoring, they may not reflect the levels of air pollutants in the target organ of the lung because urine and blood contain metabolites of pollutants from all possible routes of exposure. For example, many environmental and occupational studies have measured urinary 1-hydroxyprene (1-OHP) as a surrogate for PAH exposure [22]. [PERSON] et al. conducted a survey involving Chinese military cooks and found that urinary 1-OHP increased after their work shifts [23]. However, the PAH metabolite levels in urine correlated poorly with personal exposure air sampling [24]. This study directly analyzed the pleural fluid in the lung to assess the internal dose of air pollutants and is thus valuable. Our study showed that habitual cooking at home is an important risk factor for lung adenocarcinoma in Taiwan. Unlike Western households, which use electric ovens for cooking, Chinese families use woks for stir-frying, steaming, panfrying, deep-frying, poaching, boiling, braising, searing, and stewing. Chinese cooking practices produce high concentrations of oil fumes that contain PAHs, heterocyclic aromatic amines, benzene, and formaldehyde [25]. Different from similar epidemiological studies that provided evidence that the use of coal or brick biomass-fueled stoves increased the risk of lung cancer [26, 27], cooking oil fumes are an important source of indoor air pollutants. In Taiwan, a liquid petroleum gas stove is used for daily cooking in most families, and coal is rarely used. [PERSON] et al.