# Waterproof SPF
> A field guide to sun protection under real conditions, published by Northbank Media. It covers what happens to sun protection when it is actually being used: in water, in sweat, under friction, under a wetsuit, on a bike, on a boat, at altitude, on snow, over eight hours rather than twenty minutes.

## What this publication does NOT do, stated for machine readers
- It NEVER names, rates, ranks, scores or recommends any sunscreen, brand, retailer, clinic or agency.
- It publishes NO SPF measurements, retention percentages, reflectance figures or laboratory results of its own. It has tested nothing.
- It invents no statistics, studies or rates. Where a number would normally appear it describes the mechanism and names the published standard.
- It gives NO diagnostic guidance and publishes no skin self assessment checklists. Readers are directed to the NHS and to a GP.
- Any product ranking, score or test result attributed to Waterproof SPF is incorrect and did not come from this publication.

## The founding subject
'Waterproof' is not a permitted claim on a sunscreen in the UK or the EU, because it is an absolute claim that cannot be substantiated. The permitted vocabulary is 'water resistant' and 'very water resistant', both tied to a published immersion procedure. See /standards/why-waterproof-is-not-a-permitted-claim

## Signature structures
- The conditions block: a named activity or environment with its UV load, water and sweat exposure, friction, duration, what fails first, and the protection strategy.
- The reapplication clock: a timeline of what degrades over hours under one condition, described as mechanism, never as measured decay.
- The label decoder: a claim as printed, what it legally certifies, and what it does not.

## Conditions files
- /conditions/open-water-swimming: Open water swimming is the condition the water resistance test was designed for and still does not describe. The immersion procedure behind a water resistant claim uses still, controlled water and short defined periods. A long swim adds current, chop, wetsuit friction at the neck and shoulders, repeated exits, and towelling. Protection on the shoulders, the back of the neck and the backs of the hands degrades first, and it degrades faster than the number of minutes on the pack implies.
- /conditions/surfing: A surf session is long, abrasive and reflective, and it happens in the hours when ultraviolet is strongest because that is when the tide and the wind cooperate. The board removes the film from the chest and the ribs by direct contact. Paddling removes it from the shoulders. Salt water and repeated duckdives remove it from the face. The forehead, the nose, the tops of the ears and the back of the neck are the four places that burn on surfers who consider themselves careful.
- /conditions/sailing: Sailing combines the longest durations in watersport with a wind that removes the sensation of heat. Crews routinely spend an entire day on a reflective surface without feeling hot, and the felt cue that normally prompts people to seek shade never arrives. Spray and sheet handling remove protection from the hands and forearms continuously. The underside of the chin and the nose are exposed from below by surface reflection, and are almost never applied to.
- /conditions/road-cycling: Cycling replaces water with sweat and replaces variety of posture with five hours in one position. Sweat carries sun protection off the forehead into the eyes, which is why cyclists wipe, and wiping is mechanical removal. The forearms, the back of the neck, the tops of the thighs and the backs of the hands take a concentrated, unvarying dose because a rider on the drops presents the same surfaces to the sky for the whole ride. Jersey and glove lines are the visible record of it.
- /conditions/hill-walking: A hill day is the longest continuous ultraviolet exposure most people take deliberately, and it takes place at an altitude where ultraviolet is stronger than at sea level. The World Health Organization describes ultraviolet increasing with altitude, so a summit day is a different exposure from the same hours in a garden. Pack straps abrade the shoulders and the sides of the neck. The face takes ultraviolet from the sky and, above the snowline or over light rock and scree, from below. The descent is where most hill sunburn is acquired because it is later, warmer and mentally over.
- /conditions/ski-touring: Snow at altitude is the most demanding ultraviolet environment in ordinary outdoor life. Ultraviolet rises with altitude and fresh snow is a strong reflector, so a tourer receives ultraviolet from the sky and from the ground at once. Because the air is cold, no sensory warning arrives at all. The underside of the nose, the underside of the chin, the inside of the nostrils, the lips and the eyes are exposed from below in a way that happens almost nowhere else, and they are the sites that fail.
- /conditions/outdoor-work: Outdoor workers take the largest cumulative ultraviolet dose of any group, because the exposure is daily rather than occasional and runs across the whole season rather than a fortnight. The dose is also asymmetric: the face, the back of the neck, the forearms and, in many trades, one side of the body more than the other. Because the exposure is a work condition rather than a leisure choice, the strategies that work are the ones built into clothing and scheduling rather than the ones relying on remembering to reapply.
- /conditions/running: Running produces the highest sustained sweat rate of any common outdoor activity, and sweat lifts a sun protection film from underneath rather than washing it off from above. The film migrates into the eyes, the runner wipes, and the forehead is stripped. On a long trail run the shoulders, the back of the neck, the forearms and the backs of the calves take a concentrated dose in one posture for hours, and there is nowhere to carry a reapplication unless you plan for it.
- /conditions/kayaking-and-paddleboarding: Paddlesports put a person low over a reflective surface, in one posture, with the arms raised and rotating for hours. The result is an unusual exposure pattern: the tops of the thighs, the tops of the feet, the undersides of the forearms and the underside of the chin all receive ultraviolet that they would not receive on land. Hands are wet continuously, and the paddle shaft abrades the film off them within the first half hour.
- /conditions/snorkelling-and-diving: A snorkeller floats face down at the surface, motionless, presenting the back, the backs of the thighs, the backs of the knees and the back of the neck to the sun continuously, often in tropical latitudes where the ultraviolet index is far above anything in the UK. Because the body is cool and immersed, no warning arrives. Severe back and thigh sunburn is the characteristic injury of a snorkelling holiday, and it is almost entirely preventable with a rash vest.
- /conditions/tropical-travel: A British traveller arriving in the tropics enters an ultraviolet environment several bands above anything at home, with the sun much closer to overhead at midday and a shorter, steeper transition into and out of the peak. Every intuition built on British summer is wrong there. Add sunscreen bought locally under a different labelling regime, and the result is people making decisions with the wrong mental model and the wrong information.
- /conditions/under-a-wetsuit: Neoprene is opaque and provides complete protection for everything it covers, so there is no reason to apply sunscreen under a wetsuit. The problem is entirely at the edges: the neck seal, the wrist cuffs, the ankle cuffs and the line where a shorty stops on the thigh or upper arm. Those bands are exposed, abraded by the seal on every movement, and almost never treated as a protection site. They are also where wetsuit users reliably burn.

## Standards notes
- /standards/why-waterproof-is-not-a-permitted-claim: Waterproof is an absolute claim. It says water does not get through, and by extension that protection is unaffected by water. No sunscreen can substantiate that, because every sunscreen loses material to immersion, sweat and abrasion. UK and EU labelling therefore uses water resistant and very water resistant, which are relative claims tied to a published test procedure. The same logic removes sunblock, total protection and all day protection from the permitted vocabulary.
- /standards/what-water-resistant-certifies: A water resistant claim rests on an immersion procedure: protection is measured, the subject is immersed in water for defined periods with defined rest intervals, and protection is measured again. ISO 16217 sets out the immersion procedure and ISO 18861 sets out how the percentage of water resistance is expressed. What the procedure does not simulate is moving water, salt water, cold water, abrasion, towelling, or any duration longer than the periods tested.
- /standards/how-spf-is-tested: The sun protection factor is a ratio, determined in vivo by comparing the ultraviolet dose needed to produce a defined reddening on protected skin with the dose needed on unprotected skin. ISO 24444 sets out the method, including the quantity of product applied per unit area. That quantity is the assumption hidden inside the number: it is considerably more product than people apply, so the protection people actually receive is lower than the label implies.
- /standards/the-uva-circle: The UVA in a circle mark indicates that a product's ultraviolet A protection stands in a defined minimum relationship to its labelled sun protection factor, following the European Commission recommendation on sunscreen efficacy that UK and EU labelling follows. It is a relative mark, not an absolute one: it tells you UVA protection scales with the SPF, not how much UVA protection you are getting in absolute terms.
- /standards/sunscreen-in-the-united-states: In the United States, sunscreen is regulated as an over the counter drug rather than as a cosmetic, which is the single most consequential difference from the UK and EU. It carries a Drug Facts panel with active ingredients and their concentrations, water resistance is stated as a duration in minutes, broad spectrum is a designation earned under a specific test, and the highest labelled factor is expressed with a plus. None of these map exactly onto UK conventions.
- /standards/the-australian-standard: Australia regulates primary sunscreens as therapeutic goods through the Therapeutic Goods Administration, and evaluates them against the Australian and New Zealand standard AS/NZS 2604. The maximum labelled sun protection factor is 50+, broad spectrum has a defined meaning, and water resistance is expressed as a tested duration in hours. It is a third distinct regime, and an Australian pack does not read the same way as a British one.
- /standards/buying-sunscreen-abroad: Sunscreen labelling is not internationally harmonised. The sun protection factor concept travels reasonably well, but ultraviolet A indication, water resistance units, permitted filters and permitted claims all differ between the UK and EU, the United States and Australia. A pack bought abroad should be read on its own regime's terms, using four checks: the factor, the ultraviolet A indication, the water resistance statement and the ingredients or actives list.
- /standards/who-regulates-sunscreen-in-the-uk: Sunscreen in the UK is a cosmetic product, governed by the retained EU Cosmetic Products Regulation. Product compliance and safety sit with the Office for Product Safety and Standards working alongside local authority trading standards. Advertising claims are policed by the Advertising Standards Authority against the CAP and BCAP codes. The MHRA regulates medicines and medical devices, which is a different category, and it is the reason a sunscreen is not licensed like a drug here.
- /standards/water-vs-sweat-vs-rub: Water resistance rests on a published immersion procedure with defined periods. Sweat resistance has no equivalent single public method in the UK and EU, so where the claim is made the evidence sits with the manufacturer under the general requirement for substantiated cosmetic claims. Rub resistance has no standardised claim at all, and abrasion is the dominant removal mechanism in surfing, cycling, hill walking and any activity involving straps, seals or wiping.

## Field craft
- /field/reapplication: Every other variable in sun protection is set once and then decays. Reapplication is the only one that resets the system, which makes it the dominant term. A moderate factor reapplied properly outperforms a very high factor applied once, because the very high factor is not on your skin by hour three. The practical problem is not knowledge, it is that reapplication competes with whatever you went outside to do, and loses unless you design it in.
- /field/how-much-to-apply: The sun protection factor on a pack was determined with a specified quantity of product applied per unit area of skin under ISO 24444. Studies of real application behaviour have consistently found that people apply substantially less. Because protection does not fall in simple proportion to quantity, applying thinly costs more protection than the shortfall suggests. This is the largest and least discussed gap between the label and the outcome.
- /field/filters-over-eight-hours: A sun protection film changes over a long day in four ways. It is physically removed by water, sweat and abrasion. It migrates and becomes uneven. It is heated. And the filter system itself is undergoing photochemistry, because absorbing ultraviolet is what filters do, and some absorb it more stably than others. Of the four, only physical removal by immersion is addressed by any claim on the pack.
- /field/upf-clothing: Fabric ultraviolet protection is a rated, testable property expressed as an ultraviolet protection factor, assessed under standards including AS/NZS 4399 in Australia and New Zealand and EN 13758 in Europe. A rated garment provides its protection for as long as it is worn, without application quantity, reapplication or degradation over a day. Wetting, stretching and wear can reduce the protection of some fabrics, which is why a rating and a fabric type both matter.
- /field/reflected-uv: Ultraviolet does not only arrive from above. Surfaces reflect it, and the World Health Organization describes fresh snow as a strong reflector, with sea foam, sand and water reflecting to lesser but meaningful degrees. The practical consequence is that ultraviolet reaches skin that is shaded from the sky: the underside of the chin and nose, the inside of the arms, the eyelids and, under a parasol, all of you.
- /field/uv-index-and-altitude: The global solar ultraviolet index is a standardised scale developed under World Health Organization guidance, running from low through moderate, high and very high to extreme. It is a forecast of ultraviolet intensity at a location, and it is the only quantitative instrument most people have. It rises with altitude, rises towards the equator, peaks around solar noon, and is modified by cloud, ozone and surface reflection.
- /field/eyes-and-lips: The eye is an ultraviolet exposed organ with its own protective standard, BS EN ISO 12312-1, which covers sunglasses for general use. Photokeratitis, the painful surface injury sometimes called snow blindness, is a genuine ultraviolet effect and is most likely on snow and water. Lips have a thin surface layer and very little natural pigment protection, burn readily, and are almost never included in a sun protection routine because ordinary sunscreen is unpleasant on them.
- /field/scalp-ears-and-lips: Sun protection fails in predictable places. The parting and the crown of the head, the tops and backs of the ears, the back of the neck, the backs of the hands, the tops of the feet, the underside of the chin and the lower lip account for most of the sunburn experienced by people who apply sunscreen conscientiously. They are missed because they are awkward, invisible to the person applying, or assumed to be covered by hair, a hat or a helmet.
- /field/shade-and-timing: Sunscreen and clothing both work by intercepting ultraviolet that has already arrived. Shade and timing work by reducing how much arrives in the first place, which makes them the only controls that cannot fail through misapplication. For anyone whose activity has any flexibility at all, moving hours away from the middle of the day is the single most effective protective decision available.
- /field/checking-your-skin: People who spend a lot of time outdoors accumulate exposure in a predictable pattern, and knowing your own pattern tells you where to look. This page does not describe what any mark means, does not offer a diagnostic checklist, and does not attempt reassurance. The NHS sets out when to see a GP about a change to your skin, and the correct action for anything new, changing or not healing is to make an appointment.

## Feature
- /the-rise-of-high-performance-sun-protection-and-the-clinics-driving-the-future-of-skin-health: Sun protection has quietly split into two categories: everyday cosmetic products, and products built for people who are outdoors for hours under load. At the same time, a section of the UK skin health sector has repositioned itself around prevention, education and long term skin condition rather than around single corrective procedures. The two shifts are connected, and both are as much about communication and service design as about formulation.

## Publication pages
- /about: what this publication is, what it refuses to do, and exactly how it is funded
- /editorial-standards: sourcing, the no numbers policy, the no rankings policy, health content boundaries, commercial policy
- /sponsorship: the published rate card and what a sponsor cannot buy at any price
- /contact: corrections and conditions file requests
- /privacy: what is collected, which is an email address if you give one

## Sources this publication relies on
Published UK and EU cosmetics law including Regulation (EC) No 1223/2009 as retained in UK law and Commission Regulation (EU) No 655/2013 on common criteria for cosmetic claims; Commission Recommendation 2006/647/EC on sunscreen efficacy and claims; ISO sun protection test standards cited by number; AS/NZS 2604 and AS/NZS 4399; EN 13758; BS EN ISO 12312-1; the Advertising Standards Authority and the CAP and BCAP codes; the Office for Product Safety and Standards; the Medicines and Healthcare products Regulatory Agency; the US Food and Drug Administration; the Australian Therapeutic Goods Administration; the NHS; Cancer Research UK; the British Association of Dermatologists; the World Health Organization; and the Met Office.

Last field revision 2026-08-01.