Background: Little is known about the impact of ultraviolet exposure, climate factors and pollutants on pemphigus. Aim: To determine whether these factors are associated with pemphigus exacerbation resulting in hospitalization. Methods: The analysis used data from the 2002–2012 National Inpatient Sample in the USA, including 68 476 920 children and adults, and measurements of relative humidity (%), ultraviolet (UV) index, outdoor air temperature and particulate matter of ≤ 2.5 or ≤ 10 μm (PM2.5 and PM10). Results: Higher rates of admission primarily for pemphigus occurred during the summer and autumn months (June–November), with the highest admission rates in July and October (both 19.7 per million). There was significant statewide variation of the prevalence of hospitalization for pemphigus, with apparent hotspots located in the southwest and northeast states. Hospitalization for a primary diagnosis of pemphigus vs. other diagnosis was associated with significantly lower humidity [mean (95% confidence interval): 64.8% (63.2–66.4%) vs. 66.4% (65.6–67.3%); analysis of variance, P < 0.01) and higher temperature [58.7 (57.1–60.2) vs. 56.3 (55.8–56.7)°F, P = 0.001], UV index [6.0 (5.7–6.2) vs. 5.7 (5.6–5.7), P = 0.02], PM2.5 [12.9 (12.0–13.7) vs. 11.8 (11.5–12.0) mg/m 3 , P < 0.001] and PM10 [26.2 (24.5–27.9) vs. 23.1 (22.6–23.6) mg/m 3 , P < 0.001]. All associations remained significant in multilevel regression models that controlled for age, sex and race/ethnicity, except for ultraviolet index, which was associated with pemphigus hospitalization only for Hispanic patients [odds ratio (95% CI) for quartile 4: 2.07 (1.02–4.21)]. Conclusion: Increasing temperature, UV exposure and small particle air pollution are associated with increased hospitalization for pemphigus. Patients with pemphigus may benefit from avoidance of these potential environmental triggers.
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