After over 10 years of testing sunscreen products, at Zurko Research we are proud to announce the incorporation of the new ISO 23675:2024 in vitro method into our technical service offering. This internationally validated in vitro approach represents a significant advancement in SPF determination and reinforces our continuous commitment to ethical, reproducible, and sustainable testing methods.

Why ISO 23675?

Prolonged exposure to ultraviolet radiation (UVR) is one of the main environmental causes of skin damage, making sunscreens essential tools in public health protection. Traditionally, SPF has been evaluated using the in vivo method described in ISO 24444, which requires exposing human volunteers to UV radiation.

ISO 23675 offers an ethically and technically sound alternative: a fully in vitro methodology that maintains a high level of correlation with the traditional in vivo method, while improving standardization, reducing costs, and shortening testing times.

Method Principle and Procedure

The method is based on UV transmittance spectrophotometry of a thin film of sunscreen product applied to synthetic plates. The measurement is performed before and after controlled UV irradiation that simulates real solar exposure conditions.

Key elements of the protocol include:

• Use of two complementary types of PMMA plates (polymethyl methacrylate) to accommodate different formulations and ensure representative results.
• Automated product application using a robotic system (automatic spreading) that mimics manual spreading, ensuring uniformity and repeatability.
• Controlled UV irradiation in compliance with ISO 24444 spectral requirements.
• SPF calculation based on standardized formulas and strict quality control criteria defined by the standard.

Technical Scope and Compatible Formulations

The method is currently validated for:

• Emulsions
• Alcoholic one-phase formulations

Scientific Advantages of the New Method

Implementing ISO 23675 brings multiple benefits to sunscreen development:

• Eliminates the need for human UV exposure, complying with replacement and reduction principles in test ethics.
• Enhances inter-laboratory reproducibility by standardizing materials, application systems, and environmental conditions.
• Enables year-round testing without relying on subject availability or skin condition.
• Significantly reduces testing time and cost.
• Fully complies with European cosmetic regulations, making it a valid alternative to ISO 24444 for SPF validation in the EU market.

Strategic Implications for Manufacturers

With the adoption of ISO 23675, Zurko Research expands its sun care study portfolio, offering:

• A scientifically robust and validated alternative to the traditional in vivo SPF method.
• The ability to assess products in development stages before proceeding to more costly and invasive trials.
• An additional value proposition for ethical or responsible cosmetic marketing claims.

This method serves as an efficient tool for internal decision-making, pre-launch validation, filter innovation, and research on advanced sunscreen formulations.

Discover the full article with answers to key questions about this method — available exclusively here.

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LINK TO THE COMPLETE ARTICLE ON ZURKO RESEARCH WEBSITE: https://www.zurkoresearch.com/noticias/iso-23675-a-new-validated-standard-for-spf-determination/

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E-mail: info@zurkoresearch.com

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