ISO 24443 · In vitro
ISO 24443: in vitro UVA protection
Determines the UVA protection factor (UVA-PF) and the critical wavelength of a sunscreen by UV transmission through a thin film on roughened PMMA plates, after a controlled UV pre-exposure, using the in vivo SPF as anchor.
Advantages
Compared with in vivo UVA methods (ISO 24442) and ISO 24444
- No volunteers and no UVA exposure of human skin
- Fast (a few hours per product) and low cost
- Reports UVA-PF, critical wavelength and UVA-PF/SPF ratio in a single run
- Accounts for photodegradation
- Accepted for EU labelling (UVA logo) and by most regulatory frameworks
Limitations
- Not stand-alone: requires the in vivo SPF (ISO 24444) to scale the curve
- Does not provide the SPF itself, nor water resistance
- Sensitive to film homogeneity: spreading technique and plate roughness are critical
Principle
The UV absorbance of a thin film (1.3 mg/cm² on moulded or 1.2 mg/cm² on sandblasted PMMA) is measured from 290 to 400 nm. The initial curve is scaled by a coefficient C so that the calculated in vitro SPF equals the in vivo SPF; from this curve the initial UVA-PF is obtained and converted into a UV dose (1.2 × UVA-PF₀ J/cm²).
Each plate is irradiated with its own dose and measured again. The final UVA-PF is calculated with the PPD action spectrum over 320–400 nm, and the critical wavelength is where 90 % of the 290–400 nm absorbance area is reached. At least 4 plates are averaged (95 % CI ≤ 17 % of the mean).
How it is performed
Preparation and baseline
Single-use PMMA plates from a validated batch; blank plate with glycerine as baseline.
Application and spreading
Product applied by weight and spread until homogeneous; robotic spreading allowed since Amd 1:2026.
Pre-exposure measurement and dose
Absorbance 290–400 nm, coefficient C (valid if 0.6 ≤ C ≤ 1.6) and dose per plate.
UV exposure and final measurement
Irradiation at 27–32 °C, post-exposure absorbance, UVA-PF, critical wavelength and ratio.
EU context
For the EU UVA logo, Commission Recommendation 2006/647/EC requires a UVA-PF/SPF ratio of at least 1/3 and a critical wavelength of at least 370 nm. ISO 24443 provides both values in one run.
At ISD Research
We run ISO 24443 with a calibrated UV exposure source, an integrating-sphere spectrophotometer, controlled-temperature drying and exposure, and robotic spreading where appropriate.
Frequently asked questions
What do I need for the EU UVA logo?
A UVA-PF/SPF ratio of at least 1/3 and a critical wavelength of at least 370 nm (Commission Recommendation 2006/647/EC). ISO 24443 measures both, scaled to the in vivo SPF.
Why does ISO 24443 need an in vivo SPF?
The in vitro absorbance curve is scaled so that its calculated SPF matches the in vivo SPF (ISO 24444). That anchor makes the UVA-PF comparable to skin.
How long does it take?
A few hours per product; results are usually delivered in about one week, subject to availability.
References
- ISO 24443:2021 (corrected 2022-02) and ISO 24443:2021/Amd 1:2026. Cosmetics, Determination of sunscreen UVA photoprotection in vitro.
- Commission Recommendation 2006/647/EC on the efficacy of sunscreen products and the claims made relating thereto.
Indicative summary of the standard: it does not reproduce or replace it, nor the ISD Research SOP or the study protocol.
Other methods
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