Changing the risk spectrum of injury and the performance of sunscreen products throughout the day

Area of Science:

• Photoprotection
• Dermatology
• Spectroradiometry

Background:

• Standard sunscreen testing uses a solar simulator spectrum approximating noontime summer sunlight (UVB-dominant).
• Existing indoor testing protocols may not accurately reflect real-world sunscreen performance under diverse natural sunlight conditions.
• Outdoor trials indicate potential overestimation of sunscreen efficacy based on indoor laboratory assessments.

Purpose of the Study:

• To compare the predicted efficacy of sunscreens against various natural sunlight spectra.
• To investigate how solar angle and atmospheric conditions influence sunscreen performance.
• To quantify the deviation of sunscreen protection from labeled values under natural sunlight.

Main Methods:

• Evaluated sunscreen efficacy using predicted performance against multiple natural sunlight spectra.
• Simulated varying solar angles and atmospheric conditions to represent diverse environmental exposures.
• Compared predicted efficacy under natural spectra to standard laboratory test results.

Main Results:

• Sunscreen products consistently showed reduced protection under natural sunlight spectra compared to labeled values.
• The greatest deviation occurred when the sun was low in the sky (near the horizon).
• This reduction in efficacy can be as high as a factor of 2.0, attributed to shifts in the UVA to UVB ratio.

Conclusions:

• Standard indoor sunscreen testing may overestimate product efficacy in real-world conditions.
• Sunscreen performance is significantly affected by variations in natural sunlight spectra, particularly at low solar angles.
• The changing ratio of UVA to UVB radiation under different sunlight conditions is a key factor in reduced sunscreen protection.