Waterproof and sweatproof: two absolutes a sunscreen cannot claim

Two words that promise an absolute

Waterproof and sweatproof belong to the same family as sunblock. The suffix does the damage. Proof, in this construction, means unaffected by, and a sun protection film is not unaffected by water or by sweat.

What actually happens to a film in water is a combination of processes. Some product is removed mechanically by the movement of water across the surface. Some is carried away in the layer of water that clings to skin and then leaves with it. Some is disturbed by contact with clothing, sand or a towel. Sweat contributes by lifting product from beneath and by encouraging the wearer to wipe.

The dominant effect in ordinary use is usually not the swimming at all. It is the towel afterwards. Drying with a towel is a mechanical removal process applied deliberately to every surface of the body, and it removes far more product than an equivalent period in water. That is why guidance on reapplication after swimming is usually phrased as after swimming and towel drying rather than as after swimming alone.

The permitted word is resistant

The vocabulary that survives is water resistant, and it is a different kind of claim. Proof asserts that an effect is absent. Resistant asserts that an effect is reduced, and a claim of degree can be tested and evidenced.

Water resistance is assessed by a defined procedure: a product is applied, the treated area is immersed for stated periods with rest intervals, and the protection factor is determined again afterwards. The retained factor, expressed against the original, is what supports the claim. There are international standard methods for this and they specify the immersion protocol in detail. The mechanics of that testing are outside this publication's subject, which is what the label may say; what matters here is that the claim rests on a measurement rather than on an assertion.

The critical point for a reader is that resistance is not permanence. A water resistant product retains a proportion of its protection through a defined immersion sequence. It has not been shown to retain it indefinitely, through unlimited immersion, or after towelling.

Very water resistant and the qualified forms

Some markets use a graded vocabulary, with a second tier for products that hold their protection through a longer immersion sequence. In the United States the labelling rules require the claim to be stated with the tested duration attached, so that a pack states water resistance for a specified number of minutes rather than water resistance in the abstract.

That construction is worth noting because it does something British packs generally do not: it attaches the condition to the claim in the same phrase. A reader who sees a duration next to the words water resistant has been told the boundary of the claim. A reader who sees water resistant alone has been told that a boundary exists somewhere.

Nothing prevents a manufacturer selling in the United Kingdom from stating the tested duration voluntarily. The common criteria for cosmetic claims require that a claim allows a consumer to make an informed decision, and a claim with its condition attached does that better than one without.

Where the wording creeps

Enforcement attention in this area tends to fall on wording that reintroduces the absolute after the pack has correctly avoided it. Several patterns recur.

Imagery doing the work of a claim. The advertising codes treat the overall impression of an advertisement as the claim, not only the words. Presentation that shows a product performing through sustained immersion, or that implies no reapplication is required around water, can carry the absolute even when the copy says resistant.

The unqualified superlative. Wording such as ultra water resistant or the highest water resistance is comparative or superlative and needs substantiation against whatever it is being compared with.

Swim proof, surf proof, sport proof. These are the same construction transplanted onto an activity. They assert that an activity has no effect on the film, which is the original claim in a new coat.

Sweat resistant used loosely. Resistance to sweat is a real property and it is not the same measurement as water resistance. A claim about sweat needs evidence about sweat.

Reading a water resistance claim as a consumer

Three questions get most of the way. Does the pack say resistant rather than proof? Does it attach a duration or an immersion condition? And does it tell you to reapply after swimming and drying, which every credible instruction panel does?

If the answer to the first is no, the pack has a compliance problem. If the answer to the second is no, the claim is real but its boundary is not stated. If the answer to the third is no, the pack is omitting the single most useful instruction it could carry.

What a reader cannot do is infer a duration from the strength of the wording. There is no relationship between how emphatic a water resistance claim looks and how long the tested immersion sequence was.

Sport, sweat and the neighbouring category

A related group of products is presented for activity rather than for water, and the vocabulary shifts accordingly: sport, active, sweat resistant, workout. The underlying issue is identical. Sweat affects a film, so any claim about sweat is a claim of degree and requires evidence about sweat rather than evidence about immersion.

Two things separate the sweat case from the water case. The first is that there is no equivalently settled test convention, so a sweat resistance claim rests on whatever protocol the manufacturer used and holds in its file. The second is that sweat is usually accompanied by wiping, which removes product mechanically, and by clothing contact, which removes more.

The wording to watch is the one that borrows the credibility of the immersion test for a different proposition. A product that has been tested for water resistance has evidence about water resistance. Presenting that as evidence for performance during exercise is an evidential mismatch of the kind the common criteria for cosmetic claims are written to prevent.

Neighbouring publications cover water resistance testing and sport use as subjects in their own right. Our interest stops at what the pack may say about them.

If you are drafting it

State resistance, not proof. Attach the tested condition where you can. Keep the reapplication instruction prominent rather than in the smallest type on the back. Make sure the imagery does not carry a claim the copy has carefully avoided. And hold the immersion test report in the product information file, because the evidence has to support the claim actually made, including any duration or activity named.

A word that was removed rather than restricted

Waterproof is one of the few pieces of sun protection vocabulary that genuinely disappeared. Unlike sunblock, which survives energetically in speech and in retail listings, waterproof has largely been replaced in consumer language too, and most people now use water resistant without thinking about it.

The reason is worth noticing, because it suggests something about how claim vocabulary actually changes. Water resistant is not a euphemism for waterproof. It is a more useful description, because a reader who hears resistant asks how much and for how long, which are the right questions. A reader who hears proof asks nothing, because the word has already answered.

Where a replacement term is more informative than the term it replaces, the replacement sticks. Where it is merely more cautious, it does not. That is a reasonable working test for anyone drafting a substitute for a discouraged phrase, and it is the difference between compliance wording and useful wording.

What to take from this

Proof means unaffected, and a sun protection film is affected by water, by sweat and most of all by towelling. Resistance is the claim that can be evidenced, it is a matter of degree, and its boundary is a tested immersion sequence rather than a day at the coast.