Realistic Sunscreen Durability: A Randomized, Double-blinded, Controlled Clinical Study.

Area of Science:

• Dermatology
• Photoprotection
• Sunscreens

Background:

• Real-world sunscreen use often involves insufficient application and infrequent reapplication.
• This study evaluated the durability of sunscreens under simulated adverse conditions.

Purpose of the Study:

• To assess the longevity of sunscreen protection over an 8-hour period.
• To compare the durability of sunscreens with different Sun Protection Factor (SPF) values.
• To investigate the impact of real-life application concentrations on sunscreen efficacy.

Main Methods:

• Twenty-four participants were randomized to apply sunscreen at either 2 mg/cm2 (FDA standard) or 1 mg/cm2 (real-life).
• SPF 15 and SPF 70 sunscreens were applied to test sites, with SPF measurements taken at baseline, 3.5, and 8 hours.
• Subjects underwent moderate exercise and water immersion during the 8-hour test period.

Main Results:

• Sunscreen protection decreased by only 15-40% over 8 hours, even with exercise and water exposure.
• SPF 70 maintained an average SPF >64 at 2 mg/cm2 and >26 at 1 mg/cm2.
• SPF 15 maintained an average SPF of 13 at 2 mg/cm2 and 7 at 1 mg/cm2.

Conclusions:

• Current sunscreens exhibit significant durability on skin, resisting degradation from exercise and water exposure.
• The findings suggest that current recommended sunscreen reapplication intervals may be longer than necessary.
• Higher SPF sunscreens, even when applied at reduced concentrations, maintained a protective SPF level for extended durations.