In vitro water resistance testing using SPF simulation based on spectroscopic analysis of rinsed sunscreens

Area of Science:

• Cosmetic Science
• Dermatology
• Material Science

Background:

• Water resistance retention (WRR) is a critical performance attribute for sunscreens.
• Current standardized WRR testing is conducted in vivo, which is time-consuming and costly.
• Existing in vitro methods have limitations in accurately predicting in vivo WRR.

Purpose of the Study:

• To evaluate a novel in vitro approach for predicting sunscreen WRR.
• To compare the predictive accuracy of the new 'solution method' against a traditional 'plate method'.
• To assess the influence of different substrate materials on WRR testing.

Main Methods:

• Investigated two in vitro methods: the traditional 'plate method' and a novel 'solution method'.
• The 'solution method' uses UV transmittance of sunscreen solutions and a film irregularity model.
• Tested sunscreen application on polymethylmethacrylate (PMMA) and ethylene methacrylate acid copolymer (EMA) substrates.

Main Results:

• The 'plate method' showed no correlation between in vitro and in vivo WRR.
• The 'solution method' using EMA plates demonstrated a significant correlation with in vivo WRR.
• The correlation was particularly high for non-water-resistant sunscreens, and results were operator-independent.

Conclusions:

• The in vitro 'solution method' offers a promising advancement for predicting sunscreen WRR.
• This method provides valuable insights into in vitro sunscreen testing, despite minor discrepancies with in vivo variability.
• The 'solution method' shows potential as a reliable screening tool for sunscreen formulations.