Seasonal Variation and Meteorological Correlates of Botulinum Toxin Injections for Axillary Hyperhidrosis in Japan: A Retrospective Analysis.

Background: Primary axillary hyperhidrosis, characterized by excessive underarm sweating without an underlying medical condition, significantly impairs quality of life. While various treatments exist, botulinum toxin type A injections are widely used in Japan, especially for severe cases. Although increased sweating is commonly observed during warmer months, the relationship between treatment demand and meteorological factors remains unclear. This study aims to determine whether there are seasonal differences in the number of axillary hyperhidrosis injections in Japan and to investigate their relationship with meteorological conditions.

Methods: A retrospective, descriptive analysis was conducted using the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) from fiscal years 2019 to 2022. Monthly injection data were correlated with meteorological variables (temperature, precipitation, solar radiation, wind speed, relative humidity, atmospheric pressure) obtained from the Japan Meteorological Agency. Seasonal differences were assessed using the Steel-Dwass test, and partial correlation analysis examined associations between meteorological factors and injection numbers.

Results: The number of axillary hyperhidrosis injections peaked consistently in May and June each year, with significantly higher volumes in spring and summer compared to fall and winter (p<0.001). Partial correlation analysis revealed a strong positive correlation between all-day solar radiation and injection numbers (r=0.7193; p<0.0001), while temperature (r=-0.6052; p<0.0001) and wind speed (r=-0.441; p=0.0031) were negatively correlated. Relative humidity showed a moderate positive correlation (r=0.3626; p=0.0169). The seasonal peak preceded the hottest months, suggesting proactive treatment-seeking behavior.

Conclusions: Botulinum toxin injections for axillary hyperhidrosis in Japan display a reproducible seasonal pattern, with demand peaking in late spring and early summer. Solar radiation, rather than temperature alone, is most closely associated with treatment frequency, indicating that patients may seek care in anticipation of increased symptoms. These findings can inform healthcare resource planning and patient education to optimize the management of axillary hyperhidrosis.