What the test does and does not observe
A sun protection factor determination is a single observation of a single film. Product is applied at the specified quantity, allowed a settling period, irradiated, and the result is read. There is no second reading hours later, no interval during which the film is left to degrade, and no simulation of a day.
That is not a shortcoming of the method. The method was designed to measure a property of a formulation, and to do so reproducibly it has to hold everything else constant. Introducing time as a variable would introduce the wearer, the weather, the water and the towel, none of which can be standardised.
The consequence is that any claim about duration is a claim about something the determination never looked at. It might still be supportable by other evidence, and that evidence would have to be about persistence rather than about protection factor. In practice a claim about a whole day faces a further difficulty: the film does not survive a day in ordinary conditions, whatever the formulation does.
Why this claim is worse than the other absolutes
Sunblock overstates the mechanism. Waterproof overstates the durability against water. All day protection does something with a more direct consequence: it tells the reader not to do the thing that most improves their protection.
Reapplication is the main lever a wearer has. The mechanism is set out in the application quantity the number assumes: because attenuation through an absorbing film is not proportional to the thickness of the film, a thinned film loses protection faster than it loses material. Restoring the film restores the protection. It is the one intervention available to somebody standing on a beach.
A claim that removes the perceived need to do it is therefore not merely unsupported. It works against the reader's interest in a way that a claim about mechanism does not. That is the reason this particular wording draws attention from regulators and public health bodies in a way that some other unsupported claims do not.
Once a day, which is a claim about a schedule
A related construction presents the product as requiring only one application. It is more specific than all day protection and it is a claim about a schedule, which makes it easier to assess: the evidence required is evidence about protection retained over a stated period under stated conditions, and those conditions would have to account fully for water, towelling, clothing and abrasion.
The construction has been the subject of regulatory and advertising scrutiny in more than one jurisdiction, and the pattern of that scrutiny is consistent. The claim is judged against what a consumer will understand it to mean, and a consumer understands it to mean that one application in the morning is sufficient for the day, including through swimming and drying. Evidence that a film retains a proportion of its protection under laboratory conditions does not support that understanding.
The advertising codes are explicit that the meaning of a claim is the meaning a consumer takes from it, considered in the context of the advertisement as a whole. A claim that is technically defensible on a narrow reading and misleading on the obvious reading is a claim that fails.
The family of duration claims
Several wordings are variants of the same thing, and it is worth being able to recognise them.
Long lasting. Vaguer, and therefore harder to assess, but still a claim about persistence that requires evidence about persistence. Vagueness is not a defence: the common criteria for cosmetic claims require support for the claim as it will be understood.
8 hour protection, 12 hour protection. A quantified duration, which at least states its own boundary. The evidence would need to relate to that duration under conditions resembling use.
No need to reapply. The clearest version, and the most difficult to support for the reasons above.
Stays on. Colloquial, and it carries the same implication. The codes look at the impression created rather than the register used.
Set and forget, apply once and go. Marketing constructions that carry the claim without stating it. The overall impression rule captures them.
| Wording | Character of claim | Evidence it would require |
|---|---|---|
| All day protection | Absolute duration | Persistence across a full day in use conditions |
| Once a day | A schedule | Retained protection over the stated period, including water and towelling |
| 8 hour protection | Quantified duration | Retained protection to that period under stated conditions |
| Long lasting | Vague persistence | Support for the claim as a consumer understands it |
| No need to reapply | Instruction as claim | Evidence that the film survives the day intact |
Framework of this publication. It describes how published rules and guidance fit together and is not a measurement, a survey or a study.
Where the instruction panel contradicts the front
A recurring pattern on packs is a front of pack duration claim accompanied by a back of pack instruction to reapply frequently, after swimming and after towel drying. The two cannot both be the operative message, and the front of pack claim is the one a reader acts on.
Under the common criteria for cosmetic claims, a claim should allow a consumer to make an informed decision, and the advertising codes assess the impression created overall. A prominent duration claim contradicted in small type on the reverse is a textbook example of important information being obscured rather than given.
For anyone auditing a pack, the useful test is to ask what a reader would do differently having read the front, and whether the back is trying to undo it.
Why the claim keeps reappearing
Duration claims are commercially attractive for a reason that has nothing to do with the science. Reapplication is the friction in the category. It is inconvenient, it is easy to forget, it is difficult with children, and it means a product runs out faster. A claim that removes the friction is a claim that removes the main objection to using the product at all.
That commercial logic explains why the wording is persistent, why it reappears in softened forms after the direct version is withdrawn, and why regulators in several jurisdictions have returned to it repeatedly. It also explains why the softened forms deserve as much attention as the direct ones. A claim that avoids the prohibited phrase while conveying the same reassurance has not solved the problem, it has relocated it.
There is an argument sometimes made in defence of these claims: that a product a person applies once is better than a product they do not apply at all, so a claim that increases use is beneficial overall. It is not an argument this publication is competent to weigh, and it is not an argument the codes recognise. The requirement is that a claim is not misleading. Whether a misleading claim produces a net benefit is a question for public health bodies, and they have not been enthusiastic about it.
If you are drafting it
Claims about persistence are not impossible, they are just claims that need evidence about persistence and a stated condition. Wording that names a tested period and the conditions of the test is assessable. Wording that names a day is not, because a day is not a testable condition.
The safest position is the one the instruction panel already occupies: state the factor, state the water resistance if evidenced, and direct reapplication. It is less exciting than an absolute, and it is the only version that survives contact with the reader's actual afternoon.
What to take from this
The determination looks at one film once. A claim about a day is a claim about something never measured, it is listed among wording that should not be used, and it discourages the single behaviour that most improves real protection.