Climate, Seasons, and Skin Cancer: A 16-Year Retrospective Study of Trends in New Zealand

Abstract

Introduction: Skin cancer remains a major public health concern in New Zealand, where high ultraviolet (UV) radiation and a predominantly fair-skinned population contribute to some of the world’s highest incidence rates. While national prevalence has recently been documented, less is known about how skin cancer incidence fluctuates across months, seasons, and years, or how these temporal patterns relate to short-term environmental factors such as UV index, temperature, and rainfall. Objectives: This study aimed to quantify seasonal and long-term trends in basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and malignant melanoma (MM) diagnosed between 2009 and 2024 and to examine their associations with environmental conditions. Methods: A retrospective analysis of 24,653 biopsy-confirmed cases was conducted using clinical records from a New Zealand skin cancer clinic over a 16-year period. Monthly incidence rates were modelled with negative-binomial regression incorporating Fourier terms to test for seasonality and long-term temporal trends were evaluated. Lagged Pearson correlations (0–6 months) were calculated to assess associations between cancer incidence and environmental variables (UV, temperature, rainfall). Results: BCC and SCC showed significant seasonal peaks in late summer and early autumn, demonstrating a delayed but consistent rise following peak UV exposure over summer months, while MM displayed minimal or inconsistent seasonality. Long-term declines in BCC and SCC surgery rates may help public health advice and chemoprevention measures; MM rates remain stable. Conclusions: This 16-year analysis highlights distinct seasonal and long-term temporal dimensions in skin cancer incidence within New Zealand’s high-UV environment, with clear increases in non-melanoma skin cancer incidence (but not melanoma incidence) following summer months.