Abstract: Objective To investigate the effect of interaction between indoor air pollution and smoking on senile asthma. Methods Households in six low-and middle-income countries： China, Ghana, India, Mexico, Russia, and South Africa, were randomly selected for household surveys, and individual questionnaires were conducted among all members aged 50 years and older. Logistic regression models were used to analyze the relationship between indoor air pollution （cooking fuel, chimney facilities）, smoking （smoking status, smoking frequency, smoking duration）, and senile asthma. Multiplication and addition models were used to assess the effects of interaction between air pollution and smoking on senile asthma. Results A total of 33 327 respondents were included in the analysis, and the overall prevalence of senile asthma in six countries was 3.89% （1 296/33 327）. After adjusting for confounding factors of country, age, gender, marital status, place of residence, education level, physical activity, and family income, the risk of asthma increased among smokers compared with that of non-smokers （OR=1.18, 95% CI： 1.01-1.45）; among the participants with different smoking frequencies, those who smoked occasionally had the highest risk of asthma （OR=1.75, 95% CI： 1.33-2.30）. The interaction analysis showed that besides smoking duration and cooking fuel, there was additive interaction between indoor air pollution and smoking on senile asthma; multiplier interactions between smoking status （interaction OR=1.60, 95% CI： 1.26-2.02）, smoking frequency （interaction OR=1.61, 95% CI： 1.28-2.04）, smoking duration （interaction OR=1.69, 95% CI： 1.39-2.21） and cooking fuel were found to be correlated with the risk of asthma in the elderly. The risk of asthma was highest when two risk factors coexisted. The risk of asthma in smokers using firewood/coal/charcoal as cooking fuel was 1.43 times higher than that of non-smokers using the electricity/gas as cooking fuel （95% CI： 1.17-1.75）. Conclusion Both indoor air pollution and smoking were associated and interacted with senile asthma.

Key words: Air pollutants, Smoking, Interaction, Asthma