If you learn to read one thing on a UK sunscreen pack beyond the factor, make it this one. The UVA in a circle mark carries more genuinely useful information per square centimetre than anything else on the label, and most people have no idea what it means.
Why ultraviolet A needs its own mark
The sun protection factor is determined against a reddening endpoint, and reddening is driven principally by ultraviolet B. Ultraviolet A behaves differently: it is present in more consistent amounts across the day and the year, it penetrates deeper into the skin, and it passes through window glass in a way ultraviolet B largely does not. It contributes to photoageing and, as the public health bodies set out, to skin cancer risk.
Because the two are measured differently and matter for different reasons, a single number cannot describe both. That is the whole reason a separate indication exists. Without it, a product could carry a very large number on the front while offering comparatively poor ultraviolet A protection, and a shopper would have no way of telling.
What the mark does
UVA in a circle
What it certifies
That the product meets the recommended minimum ratio between its ultraviolet A protection factor and its labelled sun protection factor, as set out in the European Commission recommendation on sunscreen efficacy that underpins UK and EU labelling. It is the standard European indication that a product is genuinely broad spectrum rather than an ultraviolet B product with a large number on the front.
What it does not
It does not tell you the absolute level of ultraviolet A protection. Because it is a ratio, a product with a low sun protection factor can carry the mark while providing less absolute ultraviolet A protection than a high factor product that also carries it. It also tells you nothing about how long protection lasts.
The elegance of the mark is that it is a ratio. It requires that ultraviolet A protection rises with the sun protection factor, so a person choosing a higher factor for ultraviolet B reasons is not accidentally leaving ultraviolet A behind. The awkwardness of the mark is the same thing: because it is a ratio, it says nothing absolute.
The practical consequence is worth stating plainly. Two products both carrying the circle, one at a moderate factor and one at a very high factor, are not equivalent in absolute ultraviolet A terms. The mark confirms proportion, not level.
The star rating is a different thing
Many UK packs also carry a star rating for ultraviolet A, up to five stars. This is a scheme developed in the UK by a retailer and adopted widely, and it is not the same as the European circle mark. It also works on a ratio, which produces a result people find counterintuitive: a product can gain stars by having relatively strong ultraviolet A protection compared to its own ultraviolet B protection, so a lower factor product can carry more stars than a higher factor one while offering less absolute protection of either kind.
The two schemes coexist on British shelves and are frequently conflated. The practical reading is to use the circle as the pass or fail check and the stars as additional information, while remembering that both are relative.
How UVA protection is determined
ISO 24443 sets out the in vitro determination of sunscreen ultraviolet A photoprotection, and it is the method underlying the ultraviolet A protection factor used in the ratio. There is also an in vivo method in the family based on persistent pigment darkening. The essential point for a reader is that this is a measured property with a published method, not a marketing assertion.
What this means outdoors
- On a long day out, the circle matters as much as the factor. Ultraviolet A is present across more of the day and more of the year than ultraviolet B, so an eight hour hill day or a full day on the water is an ultraviolet A exposure as much as an ultraviolet B one.
- Cloud does not deal with it. Ultraviolet A is less attenuated by cloud than people assume.
- Glass does not deal with it either. Drivers and anyone working next to a window take ultraviolet A they may not be counting.
- A pack with no ultraviolet A indication at all is telling you nothing about it. That is a genuine information gap rather than an implied reassurance.
Abroad, the mark disappears
The circle is a European convention. A pack bought in the United States will instead carry a broad spectrum designation determined under the Food and Drug Administration's own test, and Australian packs work to their own standard. None of the three are directly interchangeable, which is one of the reasons a product bought abroad may not mean what a British reader assumes. See our notes on the United States, Australia and buying abroad.
Why a ratio, and not an absolute number
It is reasonable to ask why the European approach chose a ratio at all, when an absolute ultraviolet A figure would be easier to compare. Two reasons are usually given, and both are defensible.
The first is behavioural. If ultraviolet A protection were labelled with its own independent number, packs would carry two numbers, and consumers would have to reason about the relationship between them at the point of purchase. Experience with the sun protection factor suggests that a second number would be misread at least as badly as the first. Tying ultraviolet A to the factor means that one shopping decision, choosing a factor, automatically carries the other.
The second is technical. Ultraviolet A determination and sun protection factor determination are different measurements with different precision characteristics, and expressing one as a proportion of the other avoids implying a level of comparability between two independent figures that the methods may not support.
The cost of the choice is the one described above: you cannot read absolute ultraviolet A performance off a European pack. That is a genuine limitation, and it is worth knowing about rather than assuming the mark tells you more than it does.
Reading a pack for ultraviolet A in five seconds
- Look for the circle. If it is not there, you have no ultraviolet A information at all from a European pack.
- Note the factor, because the circle ties ultraviolet A to it. A higher factor with the circle means more absolute ultraviolet A protection than a lower factor with the circle.
- Treat any star rating as supplementary rather than as a substitute.
- Stop. The rest of the front of the pack is presentation.
What is not verifiable
We publish no ultraviolet A protection figures for any product and make no comparisons, because we test nothing. Nor can any shopper determine absolute ultraviolet A protection from a pack, because the marks in use in the UK are all relative. That limitation is real and is not something a better shopping technique fixes.
The one line version
The circle means ultraviolet A protection rises with the factor. It does not mean the ultraviolet A protection is high. Take the circle as a minimum requirement, choose the factor for the conditions, and remember that neither survives an afternoon without reapplication.