ISO 23675: The Evolution of SPF Testing with an In Vitro Approach

ISO 23675: The Evolution of SPF Testing with an In Vitro Approach

Accurate SPF measurement verifies that sunscreens deliver the UV protection claimed by cosmetic brands, ensuring consumer safety and regulatory compliance. Traditionally, SPF tests involved applying sunscreen to human volunteers and evaluating their skin’s response to UV exposure.

Although widely accepted, this approach has limitations, including variability in results, safety concerns, and ethical questions. Recent advancements have introduced laboratory-based (in vitro) methods, offering safer, more consistent alternatives.

ISO 23675 is a new standard developed to formalize this in vitro technique, providing clearer guidelines and improving reliability in SPF testing.

What is ISO 23675?

ISO 23675:2024 defines a standardized method for measuring Sun Protection Factor (SPF) without the need for tests on human volunteers. This method reduces unnecessary human exposure to UV radiation while improving the consistency and accuracy of SPF testing.

The standard uses polymethylmethacrylate (PMMA) plates as artificial substrates to replicate the characteristics of human skin. Two different plate types—molded and sandblasted—are used together in what's known as the "double plate" approach, providing more reliable and precise measurements.

Sunscreen application in this method is automated using a programmed robot. ISO 23675 outlines the exact movements and pressure the robot must apply, ensuring the sunscreen layer is uniform and reproducible across tests.

After the sunscreen application and a defined drying period, spectrophotometric measurements are performed to determine an initial SPF value. The plates are then exposed to controlled UV radiation, and another round of spectrophotometric measurements calculates the final SPF. This clearly defined process provides accurate, repeatable, and comparable SPF measurements, aligning with modern testing needs.

Benefits of the In Vitro Approach to SPF Testing

Using the in vitro method outlined by ISO 23675 offers the cosmetics industry several advantages:

1. Reducing Dependence on Human Testing
   Eliminating the need for volunteers to be exposed to UV radiation represents a significant advance in terms of ethics and safety. This change meets the growing demands for alternative methods that minimize risks to human health.
2. Greater Standardization and Reproducibility
   By using automated systems for product application, the method reduces technical variations associated with manual application, such as pressure differences or inconsistencies in distribution. This ensures the accuracy and repeatability of the results.
3. Agility in Achieving Results
   In vitro tests allow for faster and more efficient analysis, optimizing the development time of new products. This translates into a more streamlined process for the industry, facilitating innovation and compliance with international regulations.
4. Sustainability and Cost Reduction
   By eliminating the need to recruit volunteers and reducing the use of disposable materials, in vitro testing contributes to more sustainable and cost-effective practices within the cosmetics industry. In addition, in vitro methods can be more agile and less costly than in vivo tests, facilitating the development and assessment of new products.
5. Limitations of the Method
   Despite the significant advantages, the ISO 23675 methodology presents some limitations. The test was validated only for emulsion formulations or single-phase alcoholic products, and is not applicable to powder, stick or tablet sunscreens. In addition, the standard does not cover the assessment of water resistance, and it is necessary to complement the tests with other specific methods.

The Role of ALS in SPF Testing

ALS is a global leader in cosmetic safety and efficacy testing, specializing in static SPF, water resistance, and broad-spectrum assessments. Our dedicated SPF laboratory—a recognized Center of Excellence—uses advanced automated application technology and participates in international proficiency studies, delivering consistent, accurate, and reliable results.

With deep regulatory expertise and proactive, consultative support, ALS helps brands smoothly transition to the new ISO 23675 standardized in vitro testing method. By seamlessly integrating testing into your product lifecycle, we reduce risks, prevent costly delays, and enable faster, more confident launches—turning compliance into a competitive advantage and positioning your sun protection products for sustained growth.

Contact us today: beauty.usa@alsglobal.com or call +1 310 214-0043.