ISO 23675 · In vitro · New
ISO 23675 Double Plate: in vitro SPF
The first ISO method that determines the SPF entirely in vitro. The product is spread on two types of PMMA plate and the UV transmission is measured before and after irradiation. No volunteers, no expected SPF needed, results in about one week.
Advantages
Compared with in vivo ISO 24444
- Short test time: a few hours per product
- Lower cost: no volunteers involved
- No expected SPF required
- Takes photodegradation into account
- Every prototype can be tested, not only the finalist
Limitations
- Limited to emulsions and single-phase alcohols
- Reports SPF only (no UVA-PF or critical wavelength)
- Does not report water resistance
- Plates do not respond to anti-inflammatory ingredients, which can contribute to an in vivo SPF
Principle
A defined amount of product is spread on at least 3 moulded and 3 sandblasted PMMA plates, treated as pairs (one of each). The plate roughness simulates the micro-relief of skin: on rougher (moulded) plates the film is thinner on the peaks and the measured SPF is lower; on smoother (sandblasted) plates the film is more even and the SPF is higher. Using both brackets the behaviour of real skin.
The UV absorbance of each plate is measured with a spectrophotometer to obtain a pre-irradiation SPF. Each pair then receives a UV dose derived from that value, is measured again, and the final in vitro SPF is the mean of the pairs.
How it is performed
Preparation
Plates and product stored in the dark at a controlled temperature (27 ± 2 °C) for at least 12 h.
Weighing and spreading
1.3 mg/cm² on moulded and 1.2 mg/cm² on sandblasted plates, 3 to 10 pairs, spread with an automated robot for maximum reproducibility.
Drying
30 to 60 min in the dark at 27 ± 2 °C.
Measurement, irradiation, measurement
Pre-irradiation absorbance, UV exposure with a dose derived from the pre-irradiation SPF, and post-irradiation absorbance.
Validation
The 95 % confidence interval of the final SPF must be below 17 % of the mean.
EU context
In its 2025 market surveillance of sunscreens (JACOP 2025, final report published September 2026), the European Commission checked the SPF of 74 products with the Double Plate in vitro method, not with volunteers.
The first independent check of a product on the EU market may therefore be on a plate. If an SPF has only been measured in vivo, it is worth knowing how the formula reads in vitro.
At ISD Research
We run Double Plate with robotic spreading (Spreadmaster), a controlled-temperature chamber (Thermaster), an integrating-sphere spectrophotometer and a solar simulator, alongside ISO 24444 and HDRS, so you can see how your formula reads on a plate and on skin.
Frequently asked questions
What is ISO 23675?
ISO 23675:2024 is the international standard for determining the SPF of a sunscreen in vitro with the Double Plate method: UV transmission through thin product films on moulded and sandblasted PMMA plates, before and after irradiation.
How long does an ISO 23675 study take?
The test itself takes a few hours per product. At ISD Research, results are usually delivered in about one week, both for screening and for the full study with ISO report, subject to availability.
Which products can be tested with Double Plate?
Emulsions and single-phase alcoholic products. Sticks, powders and water-resistance claims are not yet covered; for those we use ISO 24444.
Does ISO 23675 replace ISO 24444?
Not for every case. Double Plate gives an SPF without volunteers and is well suited to screening prototypes and to checking formulas; ISO 24444 remains the reference for products and claims outside its scope, such as water resistance.
References
- ISO 23675:2024 (UNE-EN ISO 23675:2025). Cosmetics, Sun protection test methods, In vitro determination of SPF.
- Pouradier F et al. Int J Cosmet Sci 2025;47(Suppl 1):37–52. doi:10.1111/ics.13088
- European Commission, DG GROW. EU moves to more ethical sunscreen testing (JACOP 2025), 15 Sep 2026.
Indicative summary of the standard: it does not reproduce or replace it, nor the ISD Research SOP or the study protocol.
Other methods
Is this the right method for your product?
Tell us your product, claim and market. We will propose the method and option that fit.