SPF testing is the laboratory work that converts a sun-protection promise into a number you can lawfully print on a label, and for any brand placing a sunscreen or SPF day-cream on the EU market it is non-negotiable. An SPF figure is a measured efficacy claim, not a marketing flourish, and EU authorities expect it to be backed by recognised, reproducible methods before the product reaches a shelf.
This guide explains how SPF is measured, the difference between in vivo and in vitro methods, how UVA protection and the “1/3 rule” work, and how laboratory results translate into the protection categories and label claims you are allowed to use. It is written for sun-care and day-cream formulators preparing the evidence behind an SPF claim.
Key takeaways
- SPF measures protection against UVB-induced erythema (sunburn); UVA protection is assessed separately and must be balanced against the SPF.
- The reference method for SPF is the in vivo ISO 24444 test on human volunteers; ISO 24443 is the in vitro method for UVA protection.
- EU Commission Recommendation 2006/647/EC sets the UVA-PF ≥ 1/3 of SPF rule and the conditions for the UVA-in-a-circle logo and “broad spectrum” wording.
- SPF values map to four label categories: Low, Medium, High and Very high — you may never round an SPF up into a higher category.
- Every SPF, UVA and water-resistance claim must be substantiated and held in the product’s CPSR before sale under Regulation (EC) No 1223/2009.
Why SPF testing is required and the EU framework
In the EU, sunscreens are cosmetic products governed by Regulation (EC) No 1223/2009. The regulation requires that any claim made for a product is supported by adequate and verifiable evidence, and an SPF is one of the most heavily scrutinised claims a cosmetic can carry. On top of the regulation, the European Commission issued Recommendation 2006/647/EC on the efficacy of sunscreen products, which standardises how protection should be measured, expressed and labelled across the single market.
The practical consequence is simple: you cannot self-assign an SPF. The figure must come from a recognised test, the supporting report must be filed in your product information file, and the same evidence underpins the safety assessor’s review. SPF substantiation sits alongside the broader battery of laboratory testing requirements for product safety that every cosmetic must satisfy before notification.
In vivo vs in vitro: ISO 24444 and ISO 24443
SPF and UVA protection are measured by different, complementary standards. Understanding which method produces which number — and on what kind of subject — is essential when you commission a laboratory.
In vivo SPF — ISO 24444
ISO 24444 is the internationally recognised reference method for determining the Sun Protection Factor in vivo, meaning on human volunteers. A defined quantity of product (2 mg/cm²) is applied to the skin, and the minimal erythemal dose (MED) — the UV dose that produces just-perceptible reddening — is compared between protected and unprotected skin. The ratio of the two MEDs is the SPF. Because erythema is overwhelmingly driven by UVB, ISO 24444 characterises UVB protection specifically. It remains the benchmark that other methods are calibrated against.
In vitro UVA — ISO 24443
ISO 24443 determines UVA protection in vitro, using product spread on a roughened PMMA plate and UV transmittance measured spectrophotometrically before and after a controlled UV exposure. It yields the in vitro UVA protection factor (UVA-PF) and the critical wavelength. A persistent-pigment-darkening (PPD) approach to UVA exists as ISO 24442 (in vivo UVA), while ISO 16217 covers the water-immersion procedure used to support water-resistance claims. For most EU dossiers the SPF (ISO 24444) and the in vitro UVA-PF (ISO 24443) form the core pair of efficacy results.
SPF and UVA are two separate measurements. A high SPF tells you nothing about UVA performance on its own — a product can have an excellent SPF and still fail the UVA balance test, which is exactly why the EU framework requires both numbers.
UVA protection, the 1/3 rule and the UVA logo
Commission Recommendation 2006/647/EC establishes a minimum standard for balanced protection: the measured UVA protection factor should be at least one third of the labelled SPF (UVA-PF ≥ SPF/3). A product that meets this threshold — and also reaches a critical wavelength of at least 370 nm — may display the UVA logo, the letters “UVA” inside a circle, signalling that the product offers a recognised level of UVA protection proportionate to its SPF.
The same proportional standard underpins the term “broad spectrum”. In EU practice, “broad spectrum” should only be used where the product satisfies the UVA-PF ≥ 1/3 SPF rule, so the claim is a statement of measured balance rather than a loose descriptor. When you plan label wording, treat the UVA logo and any spectrum claim as outputs of the test data, not as independent marketing choices — a discipline that applies to all cosmetic claims allowed in the EU.
How SPF values map to label categories and claims
Recommendation 2006/647/EC also discourages very high numerical SPFs being presented in confusing ways and groups SPF results into four protection categories, each tied to permitted “category” wording. The labelled SPF must correspond to the category the measured value falls into — and crucially, you must label down, never up: a measured SPF of 28 is labelled as SPF 25, not 30.
| Measured SPF | Protection category | Permitted label claim |
|---|---|---|
| 6 – 9.9 | Low protection | SPF 6, SPF 10 |
| 10 – 14.9 | Medium protection | SPF 15, SPF 20, SPF 25 |
| 15 – 29.9 | High protection | SPF 30, SPF 50 |
| 50 and above | Very high protection | SPF 50+ |
Note the convention: the EU caps the highest displayed value at “50+”, because differences in measured protection above SPF 50 are marginal and difficult to communicate meaningfully. Products below SPF 6 should not carry an SPF claim or the protection-category descriptors at all.
Rounding an SPF upward is a regulatory breach. If your batch tests at SPF 28, the maximum you may claim is SPF 25 (“High protection”). Claiming SPF 30 on that result misstates a measured efficacy figure and exposes the product to enforcement, recall and reputational damage.
Water resistance testing
If you intend to claim “water resistant” or “very water resistant”, that wording is itself a substantiated claim and needs its own test. The standard approach measures SPF before and after controlled immersion in water: a product is “water resistant” if it retains at least 50% of its initial SPF after two 20-minute immersions, and “very water resistant” after four. The retained SPF — not the dry-skin SPF — is what justifies the on-pack wording, and the protocol ties back to the water-immersion procedure described in ISO 16217.
Because immersion can alter how a formulation behaves over time, water-resistance work sits naturally alongside stability testing of your cosmetic product, which confirms the SPF system performs consistently across the product’s shelf life rather than only on the day of manufacture.
“Waterproof” and “sweatproof” are not permitted descriptors in the EU. Use “water resistant” or “very water resistant” only, and only where the immersion test supports the claim.
SPF claims and the CPSR
All of these results — the SPF, the UVA-PF, the critical wavelength and any water-resistance data — converge in your documentation. The efficacy evidence has to be available to the safety assessor and reflected in the Cosmetic Product Safety Report, and a certificate of analysis for each batch helps demonstrate that the marketed product matches what was tested. Without this paper trail, an SPF claim is unsubstantiated, and an unsubstantiated efficacy claim is one of the fastest ways to attract enforcement attention during CPNP scrutiny or a market check.
Bringing it all together
A defensible SPF claim is a chain: an in vivo ISO 24444 SPF, an in vitro ISO 24443 UVA-PF that satisfies the 1/3 rule, correctly categorised label wording, any water-resistance data — all substantiated and carried through into the safety dossier. Get the testing strategy right at the start and the labelling, logo and broad-spectrum decisions follow logically from the data.
If you are preparing a sunscreen or SPF day-cream for the EU, Lexora can help you order the right batch documentation through our Certificate of Analysis (CoA) service and pull every efficacy result into a compliant Cosmetic Product Safety Report (CPSR). Talk to our team before you finalise your label, and we will make sure your SPF claim stands up to scrutiny.
Frequently asked questions
What does SPF actually measure?
SPF (Sun Protection Factor) measures how well a product protects skin against UVB-induced erythema, or sunburn. It is the ratio between the UV dose needed to redden protected skin and the dose needed on unprotected skin, determined in vivo under ISO 24444. It does not, by itself, describe UVA protection.
What is the difference between ISO 24444 and ISO 24443?
ISO 24444 is the in vivo reference method for measuring SPF (UVB protection) on human volunteers. ISO 24443 is the in vitro method for determining UVA protection (the UVA-PF and critical wavelength) using a spectrophotometer and a PMMA plate. Most EU sunscreen dossiers rely on both: one for SPF, one for UVA.
What is the 1/3 rule for UVA protection?
Under Commission Recommendation 2006/647/EC, the UVA protection factor must be at least one third of the labelled SPF. A product meeting this threshold (and a critical wavelength of at least 370 nm) may display the UVA-in-a-circle logo and be described as offering balanced, broad-spectrum protection.
Can I round my SPF up to the next number?
No. The labelled SPF must reflect the protection category your measured value falls into, and you must always label down. A measured SPF of 28 is labelled as SPF 25 (High protection), never SPF 30. Rounding upward misstates a measured efficacy claim and is a regulatory breach.
How is water resistance tested?
SPF is measured before and after controlled water immersion. A product qualifies as “water resistant” if it keeps at least 50% of its initial SPF after two 20-minute immersions, and “very water resistant” after four. The retained SPF justifies the claim. “Waterproof” and “sweatproof” are not permitted in the EU.
Where do my SPF test results need to be recorded?
All efficacy data — SPF, UVA-PF, critical wavelength and any water-resistance results — must be substantiated and reflected in the Cosmetic Product Safety Report, which forms part of the product information file held under Regulation (EC) No 1223/2009. Batch-level documents such as a certificate of analysis help show the marketed product matches what was tested.
