Ambient temperature and palmoplantar pustulosis exacerbation-related healthcare visits: a 20-year observational cohort.

Palmoplantar pustulosis (PPP) is a chronic inflammatory skin disease marked by recurrent pustules and erythema on the palms and soles. Whether ambient temperature is associated with PPP activity remains insufficiently defined. To evaluate the association between ambient temperature and PPP exacerbation-related healthcare visits. We conducted a 20-year retrospective observational study including 3,834 patients with dermatologist-diagnosed PPP treated between January 2004 and December 2024. Clinical visit data were linked to historical meteorological records according to patients' residential region and visit month. The primary outcome was defined as PPP exacerbation-related healthcare visits, an operational visit-based proxy for clinically active or suspected active PPP. Skin biopsy was performed in 47.4% (n=1,818) of patients. PPP outpatient visits and the proportion of PPP cases among all psoriasis patients peaked during summer. Compared with a simulated random distribution stratified by year and geographic region, the month of PPP exacerbation-related healthcare visits showed a shift toward higher ambient temperatures. In rank-based analyses, 47.9% (n=1,768) of visits occurred in the hottest month relative to the preceding three months. In addition, 58.6% of patients experienced an increase in ambient temperature before the PPP-related visit. Sensitivity analyses restricted to records suggestive of recurrence, progression, or treatment failure showed generally consistent temperature-related patterns. Elevated ambient temperature was associated with PPP exacerbation-related healthcare visits. These findings should be interpreted as associations rather than evidence of causality and require confirmation in prospectively defined PPP cohorts.