Evaluating the factors influencing sun protection factors (SPF): Pooling data from multiple studies involving two reference ISO 24444:2019 sunscreen products (P2 and P8).

This study adds new original data about the impact of intrinsic and extrinsic factors on SPF variations pertaining to ISO reference sunscreen P8 (SPF 50+). The findings suggest that some factors will inevitably impact the results between two SPF experiments for the same product and SPF testing laboratory. The interconnections between the sources of this variation are discussed. The findings of this research help to identify and characterize factors that contribute to SPF testing variability.