A rapid single session in vivo method to quantify blue light protection using immediate pigmentation darkening

Area of Science:

• Dermatology and cosmetic science
• Photobiology
• In vivo efficacy testing

Background:

• Blue light exposure is linked to skin oxidative stress and pigmentation changes.
• A standardized method for quantifying cosmetic protection against blue light is currently lacking.
• Existing methods for assessing blue light protection are often time-consuming.

Purpose of the Study:

• To develop a rapid, single-session in vivo method for quantifying cosmetic product protection against blue light.
• To assess immediate pigmentation darkening (IPD) induced by blue light.
• To compare the outcomes of the new method with existing multi-day protocols.

Main Methods:

• Developed a single-session in vivo assay measuring Individual Typology Angle (ITA°) changes post-blue light exposure.
• Tested 22 cosmetic formulations with varying filter types (mineral, organic, nano, non-nano).
• Calculated a Blue Light Protection Index (BLPI) based on the reduction in immediate darkening relative to controls.

Main Results:

• The BLPI demonstrated a wide dynamic range (14.6-79.2), effectively differentiating formulations.
• Mineral filters, particularly non-nano TiO2 + ZnO systems, showed higher BLPI values.
• The new method's product rankings showed good concordance with a multi-day literature protocol.

Conclusions:

• The proposed single-session IPD-based method offers a rapid, reproducible, and biologically relevant assessment of blue light protection.
• This method effectively discriminates between cosmetic formulations and aligns with established protocols.
• The approach is suitable for formulation screening and may aid in harmonizing visible light assessment methodologies.