How ISO approval of two test methods will revolutionize sunscreen development


Sunscreen testing is on the path to becoming more ethical, cost efficient, reliable (in terms of SPF measurement) and faster thanks to a recent move by the International Organization for Standardization (ISO), a non-governmental organization that develops and publishes international standards. The group has recommended two new test standards for final approval.

The standards, known as ISO 23675 and ISO 23698, represent major advancements in sun protection testing. Their endorsement is a monumental achievement, 10 years in the making. The standards are now in the final draft for international standard (FDIS) stage. The final vote, scheduled for September 2025, is expected to seal the deal.

ISO 23675 (In vitro SPF Testing)


As outlined by ISO, the 23675 in vitro SPF test method is based on UVR transmittance spectroscopy, whereby “spectrophotometric measurement of UVR transmission through appropriate UVR-transparent substrates” allows for the prediction of in vivo SPF values. “This in vitro SPF method revealed a strong reproducibility and correlation with in vivo SPF values,” ISO reported. “This in vitro SPF method revealed a strong reproducibility and correlation with in vivo SPF values,” ISO reported.

The method is applicable to sunscreen products in the form of an emulsion or alcoholic one-phase formulation, excluding loose or compressed powder or stick forms. Specifications are given to enable the determination of the spectral absorbance characteristics of SPF protection in a reproducible manner.

“Use of this method is strictly for the determination of a static sun protection factor,” ISO noted. “It is not validated for the determination of water resistance properties of a sun protection product.”

ISO 23698 (HDRS Sunscreen Testing)


The 23698 method, or hybrid diffuse reflectance spectroscopy (HDRS) method, according to ISO provides “a non-invasive optical assessment of the protection provided by topically applied sunscreen products as measured in situ on human skin as used by consumers, without requiring physiological responses and causing no physical harm to the test subject.”

Per ISO, “by combining full spectrum in vitro spectroscopic measurements of the sunscreen with optical measurements of the sunscreen transmission in the UVA on human skin, a hybrid spectrum is derived that provides full assessment of both magnitude and breadth of sunscreen protection in both the UVB and UVA regions of the sun’s spectrum, correlating closely with in vivo SPF and in vitro UVA-PF test results as demonstrated during validation of this test method.”

This method outlines a procedure to characterize the sun protection factor (SPF), UVA protection factor (UVA-PF) and critical wavelength (CW) of sunscreen products without requiring biological responses. The method has reportedly been validated for emulsions and single-phase products.

“Specifications are given to enable determination of the absolute spectral absorbance characteristics of a sunscreen product on skin to estimate sunburn and UVA protection,” the standard states. “It is applicable to products that contain any component able to absorb, reflect or scatter ultraviolet (UV) rays and which are intended to be placed in contact with human skin.” This method is presented as an alternative to the ISO 24443 and ISO 24444 methods.

Why ISO’s Approval is Exciting


Sébastien Miksa, general manager of Weneos (formerly Helioscreen), believes the endorsement of these standards is a major step forward for the industry. “This news is exciting because it represents a major advancement in sun protection testing methods, which will improve the ethical, speed, cost-efficiency and reliability of SPF measurements compared to the in vivo reference method,” he wrote.

“The journey to final approvals took so long due to the complexity of developing methods that are both robust and universally acceptable,” he added. “It required extensive collaboration, innovation and numerous validation tests to ensure the new standards met the high accuracy and reproducibility required by the industry.”

Miksa’s roles related to ISO 23675 were to envision and develop a robotic spreading technique and to publish the in vitro double plate principle that was validated by Cosmetics Europe and ISO group. He also participated in the Ring Test and supported technical aspects of it. For ISO 23698, he reports he mainly challenged the method about technical limits. Beyond these roles, he is also project leader for the ISO 24443 revision..

How it Will Impact Sunscreen Formulators


“The new SPF testing methods, ISO23675 and ISO23698, will greatly benefit sunscreen product developers,” Miksa continued. “These methods offer faster and more cost-effective testing, with improved accuracy and consistency. This will streamline the development process, reduce expenses, and ensure that products provide reliable sun protection. Consequently, developers will be able to innovate more efficiently while maintaining high standards of quality and safety for consumers.”

Next Step Toward Final Approval

As stated, the methods are expected to be officially published in September 2025.

“Once ISO standards (ISO 23675 and ISO 23698) are published, both methods will be implemented and available for assessing sun protection,” explained Miksa. “The acceptance of results or methods is ultimately determined by regulatory requirements.”

Per Miksa, in the European Union, according to the Commission Recommendation of Sept. 22, 2006, regarding the efficacy of sunscreen products and the claims made regarding them (2006/647/EC), “these alternative methods will be directly accepted because it clearly states that preference should be given to in vitro testing methods that provide an equivalent level of UVB protection.”

Miksa concluded, “The future of sunscreen testing looks incredibly promising, and I’m excited to see these advancements come to life.”

Jun 10th, 2024 Rachel Grabenhofer, C&T, with Sébastien Miksa, Weneos (formerly Helioscreen)

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