Addressing technical challenges associated with the FDA's proposed rules for the UVA in vitro testing procedure

Area of Science:

• Dermatology
• Cosmetic Science
• Analytical Chemistry

Background:

• The Food and Drug Administration (FDA) proposed in vitro testing rules for UVA protection in sunscreens.
• Initial application of these rules revealed technical challenges with roughened quartz substrates and transmittance analyzers for high SPF products.

Purpose of the Study:

• To evaluate modifications to the FDA's proposed UVA in vitro testing procedure.
• To address challenges related to substrate suitability and sunscreen application uniformity.

Main Methods:

• Two modifications were tested: using Vitro Skin N-19 as an alternative substrate and increasing sunscreen application time from 10 to 30 seconds.
• These modified conditions were used to evaluate six commercial sunscreens and two experimental prototypes.

Main Results:

• The modifications successfully met coefficient-of-variation criteria and avoided exceeding analyzer dynamic ranges.
• Commercial sunscreens achieved "medium" or "high" UVA categories based on UVAI/UV ratios.
• Experimental prototypes containing bisoctrizole and bemotrizinol achieved the "highest" UVA category (rating > 0.95).

Conclusions:

• The modified UVA in vitro testing procedure is effective for evaluating a wide range of sunscreen formulations.
• The findings support the FDA's expectation that advancements in sunscreen formulations can meet higher UVA protection categories.
• The study highlights the potential of specific UV filters (bisoctrizole, bemotrizinol) for achieving superior UVA protection, though their US regulatory status is pending.