Are there alternatives to the traditional in-vivo SPF test (ISO 24444)? Comparison and statistical analysis of 5 proposed methods

Sun protection products play a critical role in defending consumers' skin against the harmful effects of ultraviolet radiation during sun overexposure. Regular use of these products is essential, but it is equally important to ensure that the sun protection factor (SPF) communicated to consumers is accurate and allows consistent comparison between products. This is particularly vital since the vast majority of consumers base their purchasing decisions on the SPF value displayed on the label.

The current international standard for SPF testing, ISO 24444:2019, relies on testing conducted with human volunteers. Until 2024, this was the sole accepted method for SPF evaluation. However, this approach is invasive, complex, time-consuming, costly, and – as a biological test – has a high variability. Over many years, the cosmetics industry has been working to develop suitable alternative methods that give comparable results to ISO 24444:2019.

Validating such new methods is done through ring tests that benchmark the results of the new test methods against the gold standard. This requires the availability of robust in vivo reference SPF data on a large number of sun protection products – a significant experimental undertaking that cannot be repeated for each proposed method.

Recognizing this need, a consortium of sunscreen testing users and developers launched the ALT-SPF initiative in 2018 to identify, characterize, and evaluate alternative sunscreen testing methods against the ISO 24444:2019 gold standard. It included SPF testing methods that were expected to be less invasive, more precise, and more cost-effective. As part of this effort, ALT-SPF conducted an extensive study using 32 sunscreen samples. These were tested with the current ISO 24444:2019 standard and five alternative methods, including in vitro, in silico, and non-invasive in vivo testing approaches.

Each alternative method was benchmarked against the gold standard, with results analysed through statistically robust models. This rigorous approach not only evaluated the alternative methods but also laid the foundation for ISO's landmark publication in December 2024 of two alternative SPF testing methods – marking the first time non-in vivo approaches have been formally recognized as viable options to ISO 24444.

The editors, Professor Majella Lane and Professor Marc Pissavini, are honoured to welcome Mr. John Chave, Director General of Cosmetics Europe, as the guest editor of this special edition of the International Journal of Cosmetic Science. His participation underscores the importance of collaborative efforts and expertise in advancing SPF testing methodologies.

This edition features seven groundbreaking publications authored by leading experts. These papers detail the protocols, findings, and conclusions of the ALT-SPF initiative. Their contributions have been instrumental in advancing the science of SPF testing and shaping a future where innovative, reliable, and ethical methodologies take centre stage.

We hope this special edition provides you with profound insights into the future of SPF testing and underscores the importance of collaboration in driving scientific progress.

We wish you a pleasant read.

Sincerely,

The editors: