The modification effect of concentration on the correlation between ambient ozone and psoriasis: a hospital-based time-series study.

The effects of short-term ambient ozone (O) exposure on health outcomes have received growing concerns, but its effects on psoriasis is still unclear. The purpose of our study was to investigate the effects of short-term exposure to O on psoriasis, and to find out potential modifiers. A hospital-based time-series study with outpatient visit data of psoriasis was performed in Chongqing, the largest metropolitan in Southeast China. General additive models combined quasi-Poisson regression were implied to reveal the association between short-term exposure to O and psoriasis. Moreover, the potential modifiers were found out through subgroup analyses. Totally, 23,921 psoriasis outpatient visits were included. For the whole patient population, no significant association between exposure to O and outpatient visits for psoriasis was observed. Interestingly, the stratified analyses based on concentrations showed that low concentration of O (below the recommended limitation of 100 μg/m by WHO and China), rather than high concentration of O, was negatively associated with psoriasis outpatient visits at various lag days, and the greatest decrease was observed at lag03 (-2.05%; 95%CI: -3.55%, -0.53%). Moreover, stronger associations were observed in cool seasons, patients aged 40 or above, and males. Additionally, the negative associations of low-concentration O on psoriasis outpatient visits were still robust in sensitivity analyses. Our study discovered that low-concentrations of O, rather than high concentrations of O, can be associated with decreased outpatient visits for psoriasis, especially for males, population aged 40 and above, and in cool seasons.