The Effect Of Short-term Exposure To PM_2.5 On The Outpatient Visits For Acne Vulgaris:A Time-series Study

Background and purpose:Acne vulgaris（acne）is the most common skin disease on the face of young people.This disease has a prolonged course and it is easy to relapse,which seriously endangers the physical and mental health of patients.The early effective prevention and treatment is still a difficult clinical problem.The current consensus is that acne is an inflammatory disease affected by both internal and external environmental factors in individuals with genetic susceptibility.Physical factors such as ambient temperature,humidity,ultraviolet（UV）intensity and chemical factors such as smoking,occupational exposure and diet are important external environmental factors affecting keratinization,inflammation and immune response of hair follicles’sebaceous duct.In recent years,with the acceleration of urbanization,air pollution has become the primary environmental problem faced by China,and it has also been proved to be closely associated with the occurrence or development of many skin inflammatory diseases.In previous studies,benzopyrene and other substances in cigarettes can significantly promote the release of inflammatory factors in keratinocytes,and also explain the mechanism of smoking aggravating acne from the perspective of inflammation.In addition,we also carried out epidemiological investigation and research in Xi’an previously,and found that ambient particulate matter with an aerodynamic diameter less than 10μm(PM₁₀),sulfur dioxide（SO₂）and nitrogen oxide（NO₂）concentrations will significantly increase the amount of acne outpatient visits,indicating that these pollutants have the risk of increasing the occurrence or development of acne.However,among various pollutants,the relationship between PM with an aerodynamic diameter less than 2.5μm(PM_2.5)and acne is still unclear.Given that the diameter of PM_2.5 is less than PM₁₀,many studies have confirmed that it can pass through several human physiological barriers,including the blood-gas barrier,blood-brain barrier and so on,causing great harmful impacts on the human body.It can provide new ideas for the prevention and treatment of acne by investigating the relationship between PM_2.5 and acne,especially for the design of combined drugs to control the chronic inflammatory process of acne.It also lays a foundation for further experimental research and epidemiological investigation on the effects of PM_2.5 exposure on the skin.Methods:1.The daily outpatient visits for acne from December 2013 to December 2019 were collected from Southwest Hospital,Xinqiao Hospital and Daping Hospital of Army Military Medical University.By using the data of air pollutants concentrations in Chongqing from the National Environmental Monitoring Bureau and the meteorological data in Chongqing from the China Meteorological Administration,and combining with the data of acne outpatient visits,we analyzed the time-series characteristics of PM_2.5,weather variables and acne outpatient visits.We also analyzed the correlation between air pollutants and weather variables by Spearman correlation,so that we can discuss the impacts of meteorological factors on air pollution.2.We explored the correlation between air pollutants such as PM_2.5 and acne outpatient visits by generalized additive models（GAMs）.In addition,we also discussed the effect of PM_2.5 on acne outpatients after adjusting for meteorological factors.3.Sensitivity analyses of the results were also conducted.The robustness of the models was investigated by establishing two-pollutant models,changing the degree of freedoms（dfs）of important variables in the model and changing the lag time of meteorological variables in the model.Results:1.There were statistically significant correlations among environmental variables.There were significantly positive correlations among PM_2.5,SO₂,NO₂ and carbon monoxide（CO）,while there were significantly negative correlations between ozone（O₃）and them.Among these air pollutants,the concentration of PM_2.5 had seasonal fluctuation.Its concentrations were higher in autumn and winter and lower in spring and summer.This fluctuation was similar to the trend of acne outpatient visits.In addition,the average daily temperature was also negatively correlated with PM_2.5,SO₂,NO₂ and CO.The daily average relative humidity was negatively correlated with the concentrations of PM_2.5,SO₂,NO₂ and O₃,while it had positive associations with the concentrations of CO.2.There was a significant positive correlation between PM_2.5 exposure and the acne outpatient visits from lag 1 to lag 7 days and from lag 0-1 to lag 0-7 days,The most significant correlation was found at lag 0-7 day,with per 10μg/m³rise in the concentration of PM_2.5 corresponded to 1.71%（95%confidence interval（CI）:1.06%-2.36%）increase of acne visits.It indicated that the increase of PM_2.5 concentration was related to the increased risk of acne,and PM_2.5 had lag and cumulative effects on the number of acne outpatients.3.Gender subgroup analysis showed that the number of male acne outpatients had a positive correlation with PM_2.5 from lag 4 day to lag 7 day and from lag 0-4 day to lag 0-7 day.In women,such a relationship kept significant in all lag days except for lag 0 day.However,there was no significant difference in this correlation between genders,which demonstrated that there was no significant difference in the risk of acne between men and women after short-term exposure to PM_2.5.In the age subgroup analysis,the acne outpatient visits of both age groups（<25 years old and≥25 years old）were still significantly associated with PM_2.5concentrations.These correlations were most significant at lag 0-7 day.Especially,at lag 4day,such a relationship was more significant in patients over the age of 25 than that of patients under the age of 25.This indicated when patients had short-term exposure to PM_2.5,patients over the age of 25 might have a higher risk of acne visits than patients under the age of 25.4.At lag 0-7 day,the exposure-response curves of the total population and each subgroup except for the male population were approximately linear.In the female population,with the increase of PM_2.5 concentration,the risk of outpatient visits of acne patients was also increased,but the male population did not show such an obvious trend.In the age subgroups,the risk of acne outpatient treatment also increased when PM_2.5 concentrations ranged from 50to 100μg/m³.5.After establishing the two-pollutant model,changing the df of environmental variables and changing the lag time of meteorological factors,the correlation results were still statistically significant.Conclusions:1.Short-term exposure to PM_2.5 is related to the increased risk of acne outpatient visits in Chongqing,and PM_2.5 has lag and cumulative effects on the number of acne outpatients.2.Compared with people younger than 25 years old,people over 25 years old have higher risks of acne outpatient visits when they have short-term exposures to PM_2.5.3.The risks of acne outpatient visits in the male and female populations are increased after short-term exposure to PM_2.5,but there is no significant gender difference in such risks.4.This study provides indirect evidence of the correlations between PM_2.5and the occurrence or development of acne by the epidemiological investigation of PM_2.5concentration and acne outpatient visits.In order to further explore the role of PM_2.5 in the pathological mechanism of acne,basic experimental studies should be carried out in the future to reveal the relevant regulatory pathways.