Outdoor sunscreen testing with high-intensity solar exposure in a Chinese and Caucasian population

AbstractBackground

Currently, sunscreens' sun protection factor (SPF) and ultraviolet (UV) A protection are tested separately under indoor conditions, without considering external conditions that may affect performance. Studies are often conducted in Caucasian individuals; other racial groups may respond differently.

Methods

An outdoor, double-blind, intra-individual study was performed in 63 healthy Chinese and Caucasian volunteers in Singapore. Subjects underwent one outdoor sun exposure lasting 2-3 hours. ISO reference products P3 (SPF 15), P5 (SPF 30), and P8 (SPF 50+) applied at 2 mg/cm2 were compared against each other and against an untreated exposed area (positive control) and an unexposed area (negative control). Endpoints were investigator global assessment (IGA) of erythema at 24 hours, IGA of pigmentation at 1 week, and colorimetry (a*, L*, and ITA) at 24 hours and 1 week.

Results

Clinical erythema and pigmentation scores were statistically significantly different among the three sunscreens, with the highest SPF product providing the highest protection, confirming the discriminatory capacity of the model used. Colorimetric assessment correlated well with clinical evaluation.

Conclusion

This study confirmed the feasibility of ranking sunscreens (at 2 mg/cm2) based on clinical effects of high-intensity outdoor solar radiation. Larger studies are needed to look at differences in erythema and pigmentation reactions between Chinese and Caucasian individuals, which could be relevant for photoprotection.