In Vivo Measurement of UVA Protection Factor ( ISO 24442:2011) Across 38 Different SPF 50 and SPF 50+ Sunscreens Reveals High Heterogeneity and Limitations in the Level of Protection

ABSTRACT Background/Purpose The UVB and UVA components of terrestrial solar ultraviolet radiation (UVR) cause acute and chronic damage to skin. These adverse effects can be reduced by sunscreen application. The sun protection factor (SPF) is primarily a measure of UVB protection against erythema and does not quantify protection from UVA, which is the major component of solar UVR. The study aim was to assess UVA protection in relation to labelled SPF and to determine if this met the EU recommendation for a SPF/UVA‐PF ratio of ≤ 3, as recommended by the EU. Unlike SPF assessment, there is no universal consensus for the determination and labelling of UVA‐PF. Methods Thirty‐eight sunscreens with SPF ≥ 50 were selected from Europe, Latin America, Oceania, and Asia. UVA‐PF was determined with the ISO 24442:2011 in vivo method, which assesses the ability of a sunscreen to inhibit persistent pigment darkening induced by UVA radiation in a laboratory environment. Results There was variation of UVA‐PF ranging from 3.6 to 46.6. Sixty‐eight percent (26/38) of sunscreens complied with EU recommendations. Thus, about one third failed these standards, with SPF/UVA‐PF ratios varying from 3.1 (borderline failure) to 16.7 (major failure). Failure to comply was observed in several products sold in Europe. Conclusion The study demonstrates the limitations of many commercial sunscreens to reach EU standards, with significant variations in UVA protection and a lack of relationship between SPF and UVA‐PF values. This highlights the importance of improving labelling standards to ensure consumers receive consistent and adequate UVA protection, especially for those with UVA‐dependent photodermatoses. Trial Registration ClinicalTrials.gov : NCT06068010