Alternative SPF Methods on the Doorsteps

In the first two Sweep-the-Sun columns in summer 2022, we looked at the revised ISO 24444:2019 Gold standard and at the alternative methods [1, 2]. So it’s time to take another look at the progress made.

The Consortium ALT-SPF conducted the largest interlaboratory-test to date about a year ago, but the reports on the test methods involved have not yet been published [3]. Pro Memoria, the following methods were characterized against the gold standard (Table 1):

Table 1 Overview of Alternative SPF Methods in ALT-SPF Consortium [3]:

	Sun protection test methods	Standardization	since
A	GOLD STANDARD, in vivo determination of sun protection factor (SPF)	ISO 24444	2010
B	Double Plate: In vitro determination of sun protection factor	ISO/FDIS 23675	2025
C	HDRS: Sunscreen efficacy by diffuse reflectance spectroscopy	ISO/FDIS 23698	2025
D	HDRS-LED Sunscreen efficacy by diffuse reflectance spectroscopy (LED)	open
E	Fused method: “combination of the best from all methods” (ISO internal method with calibration)	open
F	In silico method Analysis of UV Filters and BASF Sunscreen Simulator or DSM Sunscreen Optimizer	open(EN 17156)

Table 2 Objective and the Workplan of the ALT-SPF Consortium [3]:

Objectives	The ALT-SPF consortium seeks to evaluate, characterize and compare alternative SPF methods that are less invasive, more precise, and more cost-effective to the current gold standard, ISO 24444:2019, and to publish the results obtained in peer-reviewed journal(s).
Sample selection	The ALT-SPF consortium selected a set of 32 sunscreen samples that represent a reasonably large spectrum of product types and SPF levels found in the market and for which the alternative methods are applicable.
ISO 24444:2019 testing	SPF samples will be tested according to the SPF in vivo method ISO 24444:2019. Each sample will be tested by four labs in two independent set-ups.
Alternative method testing	SPF samples will be tested using different alternative methods. Each sample is tested by four labs in two independent set-ups for each alternative method being evaluated (see table 1)
Statistical comparison	For each alternative method, test results will be obtained on the basis of the selected samples and compared to the test results obtained from the same samples tested with the gold standard, ISO 24444:2019.
Method characterization report	The alternative methods may show random variation together with some bias in relation to the gold standard. It is essential to characterize the methods by applying a statistical model that will make it possible to decompose total error in its different components.

The testing concept in figure 1 shows Market product types, their vehicle formats, and their residue on skin or substrate after “drying-out” (metamorphosis) [5]. Products are selected to represent the diversity of the market products (3 different vehicle format groups, no distinction is made between O/W and W/O formulations as after the vehicle metamorphosis all volatile vehicle ingredients have evaporated).

The experimental design is explained in Figure 2. Eight groups are formed (red dots). Each of these groups contains 4 market products (32 samples in total). As depicted, the SPFs 6, 15, 30, and 60 are determined with 5 different vehicle formats.

While we are eagerly awaiting the publication of the results of the ALT-SPF consortium’s round robin test on the various methods, the results were already  discussed a year ago at the working group ISO/TC 217 WG 7 (Sun Protection Test Methods). Based on these results, the two alternative methods (B and C in Table 1) have been finalized at the recent meeting in Berlin (Figure 3), so that they can move on to the FDIS stage (Final draft international standard), in which no further technical changes are possible. The future ISO standards can already be purchased at the ISO/DIS stage (Draft International Standard), but the deliberations at ISO are confidential.

If you would like to know more about the work at ISO/TC 217 COSMETICS technical committee, M. Tabari, the former committee manager, and I have written a summary of the first 25 years [6].  As chairman of ISO/TC 217, I was asked by the central secretariat in Geneva ISO/CS (iso.org) to minimize confusion in the marketplace when these two alternative SPF-methods will be introduced next year.

As we see in this recent press release from the Netherlands, there is already some confusion in the market [7]:

Consumer Association sun protection test confuses consumers

Kruidvat disagrees with the publication of the Consumers’ Association sun protection tests

Renswoude, 14 May 2024 – Kruidvat fundamentally disagrees with the recent publication of a Consumer Association test on sun protection products. This research shows that the protection factor of Kruidvat Solait Sunmilk 200ml SPF50 is lower than indicated on the packaging. This contradicts the results of studies conducted by accredited laboratories on Kruidvat’s behalf which used the same methodology as the Consumers’ Association. Tests with the exact same product showed an SPF well above factor 50. Kruidvat Solait sun protection products therefore meet the relevant safety requirements in full.

An independent safety expert has scrutinized both the Consumer Association and Kruidvat’s tests. The conclusion is that all investigations were carried out correctly. The current test uses subjects with different skin types, so the results of the studies may differ drastically from each other.

Kruidvat is calling on the Consumers’ Association and the Dutch Food and Consumer Product Safety Authority to put an end to this situation and reach joint, unanimous agreements on how to test sun protection products.

According to Niek Schipper, Trading Director of AS Watson, Kruidvat’s parent company, the difference in outcomes is bad news for consumers. “The last thing we want is for our customers to doubt the protection offered by our sunscreen products for even a second. That is why we are taking action now.”

Kruidvat has tried several times to enter into dialogue with the Consumers’ Association, but this has not led to the publication being amended nor to further investigation by the Consumers’ Association into the various test results. Kruidvat is disappointed in this lack of action.“We take quality very seriously and are confident that Kruidvat Solait sun protection products meet safety requirements in full”, says Niek Schipper

ISO’s work is scientific and thus based on scientific literature. In the “Kruidvat” case above, the large variability SPF-results of the gold standards ISO 24444 is the reason for the confusion [10]. This, has already been studied by Miksa et al some years ago [11]. They concluded that SPF results from at least three independent laboratories are required to obtain a good estimate of the true value. Next year we will be faced the case of having three SPF methods available. This is quite simple in principle. ISO 24444 will remain the gold standard until another methods is proven and established. This can only be the case after years of experience with a new alternative method. In Germany, Stiftung Warentest already has several years of experience with the “HDRS” method [12] and the Dutch authorities started using the “Double plate method” last year based on the Recommendation No. 26 of Cosmetics Europe [13]. In both cases, the results of ISO 24444 take precedence over the new method if there is a discrepancy between the two

European Level

In 2006, the European Commission adopted a Recommendation “on the efficacy of sunscreen products and the claims made relating thereto”. Twenty years later, it has begun work on revising it. At the CEAC (Cosmetics Europe Annual Conference) held in Brussels at the end of June 2024, three of those involved in the revision process explained why and how the Recommendation will be overhauled [8,9]

Global Level (ISO)

The role of ISO is to provide the scientific basis for legislations and recommendations. The standards are developed by experts, mainly from the sunscreen-, supplier- and testing-industry, as this is where most of the expertise lies. Other stakeholders such as consumer organizations or representatives of authorities are welcome and encouraged to participate in ISO, in our case in the working group ISO/TC 217 WG7 Sun Protection Testing Methods. What ISO could do to minimize the confusion on the market is to produce a guidance document discussing the benefits and limitations of the various SPF standards that will exist. This would normally take the form of a technical report (TR) and does not take as long as the development of an international standard (IS) which takes around 4 years

References:

1. SPF towards less confusion, Sweep the Sun, September 2022, https://www.ceurocosmetics-mag.com/spf-towards-less-confusion/ accessed 2024-07-25
2. Alternative SPF Methods, Sweep the Sun, September 2022, https://www.eurocosmetics-mag.com/alternative-spf-methods/ accessed 2024-07-24
3. Consortium ALT-SPF (2021) Call for interest: to evaluate alternative SPF methods. https://www.alt-spf.com  Accessed 2022-09-27
4. Surber C, Uhlig S, Bertrand C, Vollhardt J, Osterwalder U. Past, Present, and Future of Sun Protection Metrics. Curr Probl Dermatol. 2021;55:170-187. doi: 10.1159/000517667. Epub 2021 Oct 25. PMID: 34698049.
5. Surber C, Knie U. Metamorphosis of vehicles: mechanisms and opportunities. Curr Probl Dermatol. 2018;54:152–65. doi: 10.1159/000489529
6. Tabari MR, Osterwalder U, Standardization ISO and Cosmetics, in Dreher F, Jungman E, Salkamoto K, Maibach HI, Handbook of Cosmetic Science and Technology, Chapter 43, CRC 2022
7. Kruidvat, Consumer Association sun protection test confuses consumers, Press Release, Renswoude, 14 May 2024, for more information, please contact: Public Relations department, A.S. Watson Health & Beauty Benelux Telephone: 0318 579 597; e-mail: pers@nl.aswatson.com Website: www.kruidvat.nl
8. ISO 24444:2019:Cosmetics – Sun protection test methods – In vivo determination of the sun protection factor (SPF). Available from: https://www.iso.org/standard/72250.html, viewed October 12, 2020
9. Miksa S, Lutz D, Guy C, Delamour E. Sunscreen sun protection factor claim based on in vivo interlaboratory variability. Int J Cosmet Sci. 2016 Dec;38(6):541-549. doi: 10.1111/ics.12333. Epub 2016 May 18. PMID:27079525.
10. Stiftung Warentest (2020) Stiftung Warentest. https://www.test.de/Sonnen-creme-Kinder-Test-4722079-4722082/.Zugegriffen: 15.Dez.2021
11. Cosmetics Europe Recommendation No. 26 on the use of alternative methods to ISO 24444:2019, 2022-03-23, Viewed 5.5.22.
12. European Commission. Recommendation on the efficacy of sunscreen products and the claims made relating thereto. J Eur Union. 2006;245:39–43
13. Revision of the European Commission’s ” Sunscreen Products ” Recommendation Monday, July 15, 2024 Congresses, https://cosmeticobs.com/en/articles/congresses-48/revision-of-the-european-commissions-sunscreen-products-recommendation-8211