Two bands, two different kinds of damage
Ultraviolet reaching the earth's surface is conventionally divided into two bands that matter for skin. UVB occupies the shorter wavelengths and carries more energy per photon. It is absorbed in the outer layers, causes sunburn, damages DNA directly and is the principal driver of the common non melanoma skin cancers. Its intensity varies enormously with season, latitude, time of day and cloud, which is why you can burn in twenty minutes in July and not at all in January.
UVA occupies the longer wavelengths, penetrates further into the dermis, and is far more constant. It varies much less through the day and across the year, passes through cloud more readily and passes through ordinary window glass almost unimpeded. It generates damage largely through reactive oxygen species rather than direct absorption, degrades collagen and elastin over years, and drives pigmentary responses including melasma.
The practical translation is that UVB is the reason you burn on a beach and UVA is the reason a lifetime of commuting shows on the side of a face nearest the car window. Both need covering, and only one of them is described by the SPF number.
The UVA in a circle mark
The single most useful symbol on a UK sunscreen is the letters UVA printed inside a circle. It is not decorative and it is not a brand device. It signifies that the product's UVA protection factor, measured by a separate standardised method, is at least one third of its labelled SPF.
That ratio requirement is what makes the mark meaningful. It scales with the SPF, so an SPF 50 product carrying the mark must deliver substantially more UVA protection than an SPF 15 product carrying the same mark. It is a proportional guarantee rather than an absolute one.
If a product has no circled UVA mark and no star rating, you have no information at all about its UVA performance. Treat that as a reason to choose something else. It costs nothing to check and it is the fastest quality filter available to a shopper standing in an aisle.
The UK star rating system
Alongside the circled mark, many UK products carry a star rating from zero to five. This system was developed in the United Kingdom and is widely used here, which is why it appears on British packs and rarely on continental ones.
The stars express the ratio of UVA protection to UVB protection rather than an absolute level of UVA defence. This produces a result that catches people out. A four star SPF 15 product offers less absolute UVA protection than a four star SPF 50 product, because the ratio is applied to a smaller base. Stars tell you about balance. SPF tells you about magnitude. You need both numbers to know what you are getting.
The practical guidance from UK cancer charities and dermatology bodies has settled on at least SPF 30 with at least four stars for general use, and that combination remains a sound rule. For children, five stars with SPF 50 is the safer target, as covered in our children's sunscreen review.
The PA system on imported products
Sunscreens imported from Japan and Korea, which many people now buy for their textures, carry a different UVA notation: PA followed by between one and four plus signs. This grades the product by persistent pigment darkening, a method that measures how much a UVA dose tans rather than reddens the skin.
The grades map to bands of the persistent pigment darkening protection factor. PA+ corresponds to a factor of roughly two to four, PA++ to four to eight, PA+++ to eight to sixteen, and PA++++ to sixteen and above. There is no exact conversion to the European system because the measurements differ, but as a working comparison, a European product carrying the circled UVA mark at SPF 50 sits broadly in the PA++++ territory.
One caution applies to imported sunscreens generally. The permitted filter lists differ between jurisdictions, so an imported product may contain filters not approved for sale in the UK, and it will not have been assessed under UK cosmetic safety rules. That does not make it unsafe, but it does mean the usual UK enforcement chain does not apply to it.
What broad spectrum means, and does not
Broad spectrum is used loosely in marketing. In the European and UK context it should be read as shorthand for meeting the UVA to SPF ratio requirement, in other words the same thing the circled mark signifies. It is not a separately tested claim with a distinct threshold of its own.
Neither system covers visible light, which sits beyond the ultraviolet range and contributes to pigmentation in melanin rich skin. No clear sunscreen filters visible light. Iron oxide pigments in tinted formulations do, which is why tinted products score higher in our review of sunscreens for deep skin tones.
Reading a label in ten seconds
The sequence that works in a shop is short. Check the SPF number is 30 or 50. Check for the UVA in a circle mark or four to five stars. Check for a water resistance claim if you will swim or sweat. Then, if you have reactive skin, read the ingredient list for fragrance. Everything else on the front of the pack is presentation.
For official UK guidance on what to choose and why, the NHS sunscreen and sun safety page and the British Association of Dermatologists sunscreen fact sheet are the two references worth bookmarking. Neither sells anything, which is the point.