Guide
The new SPF methods: Double Plate (ISO 23675) and HDRS (ISO 23698)
In December 2024 ISO published two new methods to determine the SPF without sunburning volunteers. In June 2025 Cosmetics Europe recommended giving them preference. This guide explains what they are, how they differ from the classic ISO 24444 and which one fits each case.
Why there are new methods
The reference method, ISO 24444, determines the SPF by inducing a minimal erythema on the backs of 10 to 20 volunteers. It is slow, costly, requires supervision and shows more inter-laboratory variability than instrumental methods.
With the support of the European Commission, which explicitly encouraged alternatives to in vivo SPF testing, the industry developed methods that do not sunburn volunteers. The result is two standards published in December 2024: ISO 23675 and ISO 23698.
The three SPF methods compared
| ISO 24444 | ISO 23675 Double Plate | ISO 23698 HDRS | |
|---|---|---|---|
| Type | In vivo | In vitro | Hybrid (skin + plate) |
| Volunteers | 10–20, two sessions | None | 10–20, one session of about 60 min |
| Erythema (sunburn) | Yes, minimal and localised | No | No (dose < 5 % of a MED) |
| Results | SPF | SPF | SPF, UVA-PF and critical wavelength |
| Products | All galenic forms | Emulsions and single-phase alcohols | Emulsions and single-phase products (no powders) |
| Water resistance | Yes (with ISO 16217 / 18861) | No | Not yet |
| Photodegradation | Implicit on skin | Included | Included |
| Expected SPF | Required | Not required | Not required |
| Delivery at ISD (full study) | 3–4 weeks | About 1 week | 2–3 weeks |
Indicative times, subject to availability; an urgent service is available. Summary of the standards: it does not replace them.
Which method should you choose?
- Comparing R&D prototypes
- Double Plate (emulsions) or an HDRS screening. Fast, lower-cost results, without an ISO report when you only need to decide.
- SPF and UVA claims in one study
- HDRS: SPF, UVA-PF and critical wavelength together, without erythema.
- EU UVA logo
- ISO 24443 (in vitro, anchored to the in vivo SPF) or HDRS. Requirements: UVA-PF/SPF ≥ 1/3 and critical wavelength ≥ 370 nm.
- Sticks, powders or water resistance
- ISO 24444, with ISO 16217 and ISO 18861 for water resistance.
- Knowing how a market check will read your product
- Double Plate: the method the European Commission used in its 2025 market surveillance.
Status in the European Union
- Cosmetics Europe Recommendation No. 26 (23 June 2025): recommends that preference be given to the new non-invasive reference methods, ISO 23675:2024 and ISO 23698:2024.
- JACOP 2025 market surveillance (European Commission, report published September 2026): the SPF of 74 sunscreens was checked with the Double Plate method, not with volunteers. The first independent check of a product may therefore be on a plate.
- UVA logo: Commission Recommendation 2006/647/EC requires UVA-PF/SPF ≥ 1/3 and a critical wavelength ≥ 370 nm. HDRS gives both values together with the SPF.
Do they give the same SPF as ISO 24444?
Published validation shows agreement on average with ISO 24444 for both methods. Differences can appear for specific formulas: plates do not respond to anti-inflammatory ingredients, and HDRS can differ for low-SPF and mineral products. We therefore recommend measuring that offset on your own portfolio before switching methods.
All three SPF methods under one roof
At ISD Research we run ISO 24444, ISO 23675 and ISO 23698 in routine, together with ISO 24443, ISO 24442 and water resistance. We can measure the same formula with several methods, explain the differences and recommend the one that fits each decision: comparing prototypes, substantiating a claim or checking a specific property.
Frequently asked questions
What are the new SPF test methods?
ISO 23675:2024 (Double Plate, in vitro) and ISO 23698:2024 (HDRS, hybrid). Both were published in December 2024 and neither induces erythema in volunteers.
Do they replace ISO 24444?
Not entirely. Cosmetics Europe recommends giving them preference, but ISO 24444 is still needed for products and claims outside their scope, such as sticks, powders and water resistance.
Which method is fastest?
Double Plate: the test takes a few hours and at ISD results are delivered in about one week. HDRS needs about 60 minutes per volunteer and is delivered in 2–3 weeks.
Which method also gives UVA protection?
HDRS (ISO 23698) gives SPF, UVA-PF and critical wavelength in the same study. Double Plate gives the SPF only; for UVA it is combined with ISO 24443.
Where can these methods be performed in Europe?
ISD Research in Barcelona, Spain, runs all three ISO SPF methods (ISO 24444, 23675 and 23698) in routine.
Sources
- ISO 23675:2024. Cosmetics, Sun protection test methods, In vitro determination of sun protection factor (SPF).
- ISO 23698:2024. Cosmetics, Measurement of the sunscreen efficacy by diffuse reflectance spectroscopy.
- ISO 24444:2019 + Amd 1:2022. Cosmetics, Sun protection test methods, In vivo determination of the SPF.
- Cosmetics Europe. Recommendation No. 26 on the use of alternative methods to ISO 24444:2019, 23 June 2025.
- European Commission, DG GROW. EU moves to more ethical sunscreen testing (JACOP 2025), 15 September 2026.
- Commission Recommendation 2006/647/EC on the efficacy of sunscreen products and the claims made relating thereto.
- Pouradier F et al. Int J Cosmet Sci 2025;47(Suppl 1):37–52. doi:10.1111/ics.13088
- Ruvolo E et al. Int J Cosmet Sci 2025;47(S1):53–77. doi:10.1111/ics.13089
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