Four words behind the numbers
A British sun protection pack usually carries a numeral and, next to it or beneath it, a category word. Those words are not decorative and they are not chosen by the manufacturer freely. They come from the European Commission recommendation on the efficacy of sunscreen products and the claims made relating to them, which groups the factors into four categories.
The recommendation sets out low protection, medium protection, high protection and very high protection, and assigns a recommended set of printed factors to each. The intention is that a reader who does not want to interpret a reciprocal relationship has a plain word to read instead, and that the plain word is consistent across products.
| Category | Printed factors | What the category word tells you |
|---|---|---|
| Low protection | 6, 10 | Protection against reddening at the bottom of the scale |
| Medium protection | 15, 20, 25 | A substantial step up from low in absolute terms |
| High protection | 30, 50 | Small fractions of erythemally effective radiation reaching skin |
| Very high protection | 50+ | Above the top of the printed scale, not further distinguished |
Categories and printed figures follow the European Commission recommendation on the efficacy of sunscreen products and the claims made relating thereto.
Why only some numbers appear
You do not see a factor of 37 on a pack, and there is a reason. The recommendation sets out a limited list of figures to be printed, so that products are grouped rather than differentiated to a precision the test cannot support.
This follows from the nature of the measurement. A sun protection factor is a panel mean with a calculated confidence interval, and the interval is not narrow. Two products whose tested results differ by a few points may not be distinguishable at all. Printing every tested value would present differences that the method cannot resolve as if they were real, which is exactly the kind of false precision that labelling conventions exist to prevent.
Rounding down to the nearest permitted figure also builds in a margin. A product tested somewhat above 30 is labelled 30, not 34, so the printed figure is a conservative statement of the tested result rather than a flattering one.
The cap at 50 plus
The recommendation goes further at the top of the scale and recommends that anything above a factor of 50 is labelled 50 plus rather than with a higher figure. Three reasons stand behind that, and they compound.
The effect flattens. Because the factor is a reciprocal, the absolute difference between one fiftieth and one hundredth of the erythemally effective dose is small. The numeral would double; the change in what reaches skin would not be anything like a doubling. This is the arithmetic set out in why SPF and protection are not proportional.
The measurement gets harder. Determining very high factors requires larger ultraviolet doses on the protected site and produces proportionally wider confidence intervals. The higher the figure, the less confident the distinction between one high figure and another.
The communication risk grows. A large numeral on a pack does work that its measurement cannot support. It reads as a level of safety, and there is a long standing concern in public health guidance that a higher figure changes behaviour rather than only changing exposure. That is discussed in what the label says and what people hear.
The cap is therefore a deliberate refusal to let the scale keep rising into a region where the numerals separate faster than the effects do.
The status of the recommendation
It is worth being exact about what kind of instrument this is, because it is often described as a rule and it is not one.
A Commission recommendation is not a regulation. It does not create a binding legal obligation in the way that the cosmetics regulation does. What gives it force in practice is that the general obligations do bind: a claim must be truthful and supported, a product must be safe, and advertising must not mislead. A manufacturer departing from the recommendation is not automatically in breach of anything, and would need to explain how its labelling meets the general obligations while diverging from the reference point everyone else uses.
In practice, the categories, the permitted figures, the cap and the circled ultraviolet A mark are all followed as though they were rules, which is why they look like rules on a shelf. The distinction matters when a business is deciding what it can and cannot do, and it is set out further in the European recommendation behind the label.
Reading a category word
The category word is more useful than it looks, because it is the only part of the protection labelling designed to be read without interpretation. High protection means the same thing on every pack that carries it, which is more than can be said for most descriptive wording in this category.
What the word does not do is describe ultraviolet A protection, which is carried by the circled mark and the star rating, or describe performance in use, which depends on how much is applied. A product can be very high protection and deliver considerably less than that in practice, which is not a labelling failure so much as a limit on what any label can do.
Where category words meet other vocabulary
The four category words are the only descriptive vocabulary on a sun protection pack with a fixed reference behind them. Every other descriptive word on the same pack, and there are usually several, has no defined meaning at all.
Words such as gentle, kind, suitable, advanced, ultra, sensitive and children's sit alongside a rigorously defined numeral and an equally rigorously defined category word, and none of them corresponds to a threshold, a test or a standard. They are governed by the general requirement that a claim be truthful and supported by the evidence held, which is a real constraint, but it is a constraint of a completely different character from a printed scale with rounding rules.
This adjacency is one of the most consistent sources of confusion on a sun protection pack. A reader has no reason to know that two words printed in the same typeface, half an inch apart, sit on entirely different regulatory footings. What the categories and factors mean is fixed; what the adjectives mean is a matter of evidence held by a manufacturer that a reader will never see. The vocabulary that has no fixed meaning is covered in children's and sensitive wording and in dermatologically tested and other pack claims.
The pressure at the top of the scale
There is persistent commercial pressure to signal something above very high protection, because very high is the ceiling and a ceiling is uncomfortable for anyone trying to differentiate. The forms that pressure takes are recognisable: superlatives attached to the category word, invented tiers, wording implying completeness, and typographic emphasis that makes the plus sign look like a multiplier.
All of them run into the same problem. The scale stops where it stops because the measurement stops resolving differences, so any signal of a level above the ceiling is a signal that no test supports. A claim that cannot be substantiated fails the common criteria for cosmetic claims and, in advertising, the requirement that objective claims are capable of substantiation.
A note for people writing labels
The category word and the figure should agree, and the figure should be one of the recommended values. Wording that sits between categories, that invents an intermediate description, or that uses a superlative not in the recommendation, invites the question of what evidence supports the departure. Where wording implies a level above very high, it runs directly into the reason the cap exists.
What to take from this
Four category words, a limited list of printed figures, rounding down, and a cap at 50 plus. The structure exists to stop the label expressing distinctions the test cannot resolve, and to stop a rising numeral being read as a rising level of safety.