Association Of Environmental Exposures With Allergic Skin Diseases In Chinese Adolescents

BackgroundAllergic skin diseases are most common skin disorders.Few studies have shown that allergic skin diseases are correlated with environmental exposure.However,there is still a lack of studies on the association between environmental exposure and allergic skin diseases based on the large-scale adolescent population.ObjectiveThis study aimed to evaluate whether long-term exposure to environmental factors such as temperature,relative humidity,and air pollutants could increase the prevalence of allergic skin diseases in Chinese adolescents.Allergic skin diseases were mainly investigated:atopic dermatitis（AD）and urticaria.MethodThis study was a cross-sectional study using cluster sampling.The survey was conducted in September 2018 and included newly enrolled college students（representative of the adolescent）from five universities in different geographical locations in China（Changsha,Wuhan,Urumqi,Hohhot,and Xiamen）.Among them,skin diseases were diagnosed by professionally trained dermatologists.The diagnosis of AD was based on the guidelines of the American Academy of Dermatology.The diagnostic criteria for chronic urticaria（CU）were suffering from wheal or angioedema,and symptoms were lasting more than 6 weeks.Dermographism was diagnosed when a dermatologist performs a test on the forearm of students using a clean cotton swab.Within 10min after the test,if there was a wheal with a width greater than 3 mm at the test site,it was defined as a positive result.The auxiliary investigator assisted the dermatologist to measure the blood pressure,weight,height,and other relevant indicators of each individual.Demographic data,disease history,and living habits were collected through online questionnaires.Temperature（℃）,relative humidity（%）,and concentrations of six core air pollutants including SO₂（Sulfur dioxide,μg/m³）,O₃（Ozone,μg/m³）,CO（Carbon monoxide,mg/m³）,NO₂（Nitrogen dioxide,μg/m³）,PM₁₀（Inhalable particulate matter,μg/m³）and PM_2.5（Fine particulate matter,μg/m³）)were extracted from the Chinese Air quality Reanalysis dataset from 2013 to 2018（6 years before baseline survey）.Monthly surface BC concentrations were obtained from the National Aeronautics and Space Administration（NASA）with high resolution.Survey data were linked to the above environmental data by the respondents’home address（city or county code）.Then,the following procedure was used to adjust the respiratory rate to estimate the average daily environmental exposure of individuals:（1）calculate the mean concentration of air pollutants from 2013 to 2018;（2）estimate BMR（Basal metabolic rate）by individual sex and age;（3）evaluate the METs（Metabolic equivalents）for school time（supposing 40 h per week for all）,physical exercise（type,frequency,and duration）and sleep;（4）adjust BMR by METs;（5）estimate the METs-weighted respiratory rate;（6）estimate averagely daily exposure to pollutants according to the 6-year mean concentrations and respiratory rate.R software 4.04 was used for statistical analysis.The R software package"lme4"was used to fit the mixed effect logistic model using the random-effects model at the district or county scale.The effect sizes were presented as a ORs（Adjusted odds ratios）and 95%CIs（Confidence intervals）.A P value<0.05 was considered statistically significant.ResultIn 2018,27144 students were newly enrolled in the five universities,of whom 20,049（73.8%）signed the informed consent and completed the dermatological examination and questionnaire.Among them:（1）1281 individuals were diagnosed with AD,with a crude prevalence of 6.4%.The proportion of females in the AD was significantly higher than that of males（P=0.012）,and the prevalence of AD was significantly higher in the group with high annual household income（P<0.001）and high educational level of parents（P=0.001）than in the control group.In contrast,there were no significant differences between AD and healthy controls in terms of body mass index（BMI）,smoking,alcohol-drinking,or exercise frequency.After adjusting for covariates,the prevalence of AD is significantly associated with CO（a OR=5.02,per 1 mg/kg·d increment,P<0.001）,NO₂（a OR=1.05,per 1μg/kg·d increment,P<0.001）,PM_2.5（a OR=1.05,per 1μg/kg·d increment,P<0.001）,PM₁₀（a OR=1.03,per 1μg/kg·d increment,P=0.006）,BC（a OR=1.43,per 1μg/kg·d increment,P<0.001）,relative humidity（a OR=1.02,P<0.001）and temperature（a OR=1.05,P<0.001）.Additionally,the results shown a marginal significant correlation with SO₂（a OR=1.03,per 1μg/kg·d increment,P=0.078）,and PM₁₀（a OR=1.01,per 1μg/kg·d increment,P=0.087）.（2）CU was diagnosed in 381 students,with a crude prevalence of1.9%.There was no significant difference in the ratio of males compared with females in the CU population（P=0.269）,and the prevalence of CU was significantly higher in the group with relatively higher annual household income（P<0.001）and higher educational level of parents（P=0.001）.However,this study found no significant differences between CU and healthy controls in BMI,age,smoking,alcohol-drinking,and exercise frequency.After adjusting for covariates,CU is significantly associated with CO（a OR=5.36,per 1 mg/kg·d,P=0.050）,PM_2.5（a OR=1.04,per 1μg/kg·d,P=0.018）,BC（a OR=1.68,per 1μg/kg·d increment,P<0.001）,relative humidity（a OR=1.01,P=0.008）and temperature（a OR=1.05,P=0.004）.Furthermore,there was a marginally significant correlation between CU and NO₂（a OR=1.04,per 1μg/kg·d,P=0.082）as well as PM₁₀（a OR=1.02,per 1μg/kg·d,P=0.075）.On the contrary,no significant correlation was found between prevalence of CU and SO₂（P=0.302）.（3）Dermographism test was completed in three schools（Changsha,Xiamen,and Hohhot）,involving a total of 11,098 individuals,1722 of whom were diagnosed with dermographism for results positive,and the crude prevalence rate was 15.5%.The proportion of males was significantly higher than that of females（P=0.012）,and the prevalence of dermographism was higher in the group with higher annual household income（P<0.001）,higher educational level of parents（P<0.001）,smoking（P=0.003）and alcohol-drinking（P=0.034）,but then we found no significant differences in BMI between dermographism and healthy controls.After adjusting for covariates,the prevalence of dermographism was correlated with CO（a OR=20.12,increment per 1 mg/kg·d or a OR=1.35 per 0.1 mg/kg·d increment,P<0.001）,SO₂（a OR=1.10,increment per 1 ug/kg·d,P<0.001）,NO₂（a OR=1.07,increment per 1 ug/kg·d,P<0.001）,PM_2.5（a OR=1.05,increment per 1 ug/kg·d,P<0.001）,PM₁₀（a OR=1.03,increment per 1 ug/kg·d,P<0.001）,BC（a OR=1.64 per 1μg/kg·d increment,P<0.001）,relative humidity（a OR=1.01,per 1%increment,P<0.001）and temperature（a OR=1.26,per 1°C increment,P<0.001）.ConclusionThe prevalence of AD,CU,and dermographism is high in Chinese adolescents,and the prevalence is related to long-term exposure to environmental factors such as temperature relative humidity,and air pollutants.