We put SPF sun creams to the test – a £2.80 bargain beat a £46 bottle but warning made me question everything

SLATHERING on the factor 50 every morning makes me feel virtuous, but the truth is, I have no idea whether it’s actually doing its job. It is supposed to protect against everything from premature ageing to skin cancer – but what if there was a clever and affordable way to check if it was working? Siobhan O’Connor gets ready for the viral SPF sticker test, which can indicate that it could be time to reapply your sunscreen Credit: Euan Danks The so-called ‘magic’ UV stickers going viral on TikTok on Siobhan’s arm Credit: Euan Danks Despite being arguably the most important step in my beauty routine, there is no obvious way of knowing when the sunscreen has started to wear off. The NHS recommends reapplying sunscreen every two hours, as well as after swimming, sweating or towel drying. But in reality, it’s all too easy to lose track of when you last topped up, particularly when you’re spending an entire day outside. According to Cancer Research UK, only 60 per cent of UK adults who use sunscreen apply it before going out in the sun, and only 37 per cent take it with them to reapply throughout the day. As Britain swelters in its fifth heatwave, with temperatures reaching a sizzling 36°C today and the UV Index hitting dangerous high levels, staying protected from those rays has never been more urgent. So when I spotted so-called ‘magic’ UV stickers going viral on TikTok for their clever colour-changing abilities, I was intrigued. Videos showed people using the UV-detection patches to put different sunscreens to the test over the course of several hours, with clips collectively racking up more than a million likes. These tech-based stickers have a photosensitive layer that changes colour when exposed to both UVA and UVB rays, indicating that it could be time to reapply your sunscreen. One sticker brand, Beame, promises “no more guessing if your SPF still works” on its website. Costing £10 for 36 stickers, the small, flower-shaped patches start off transparent. You stick one onto clean skin, then apply your usual sunscreen over the top at the same time as the rest of your body. But when enough UV rays begin to reach the patch, it darkens, giving you a visual prompt that it could be time to reapply. Unlike most other skin stickers such as pimple patches, these are sweat and water-resistant, meaning you don’t need to worry about them peeling off. And with shelves packed with SPFs at wildly different price points, all promising to keep our skin protected, I wondered whether the stickers might reveal any noticeable difference between them. So I picked eight popular factor 50 sunscreens, ranging from supermarket own brands to a premium formula. Would spending more mean better staying power, or could one of the cheapest bottles hold up just as well? To find out, I lined eight UV stickers along my upper arms – four on each side – and covered each with a five-pence-piece-sized amount of a different sunscreen. My line-up ranged from bargain buys, including Aldi Lacura at just £2.80, to high-street favourites from Nivea, Simple, Boots, Superdrug and La Roche-Posay, alongside pricier formulas from Supergoop! and Trinny London – the latter costing a budget-busting £46. Then, with all eight exposed to the same conditions, it was time to head out into the sunshine. By this point, the sunscreens had been sitting on the stickers for around an hour while I finished getting ready, and every single one was still transparent. The beauty editor says the test showed her we shouldn’t assume an expensive SPF is automatically doing a better job Credit: Euan Danks WHAT I TESTED LEFT ARM First patch [top of the arm]: Trinny London See The Light SPF 50+ Moisturiser 50ml, £46. Second patch: La Roche-Posay Anthelios Uvmune 400 SPF50 50ml, £15.75 Third patch: Nivea Protect & Moisture SPF50 200ml, £6.89, Fourth patch: Simple Hydrating UV Fluid SPF50 40ml, £6.49. RIGHT ARM First [top right]: Aldi Lacura SPF50+ 50ml, £2.80 Second: Supergoop Unseen Sunscreen SPF50+ 50ml £36.50, Third: Superdrug B.Skincare SPF50 Moisturiser 75ml, £10 Fourth: Boots SPF+ Hyaluronic Acid Moisturising Lotion SPF50 50ml, £8 I’ll admit, I was starting to wonder whether the experiment would work at all. But within roughly 10 minutes of stepping out onto a sun-drenched London terrace at lunchtime, that changed dramatically. Three of the four stickers on my left arm began turning purple. The most striking was the patch covered with Trinny London’s £46 SPF50+, which quickly turned a deep purple – supposedly indicating that UV rays were penetrating the cream and reaching the sticker. Trinny London See The Light SPF 50+ Moisturiser 50ml, £46 Credit: Screengrab La Roche-Posay Anthelios Uvmune 400 SPF50 50ml, £15.75 Credit: Screengrab The Nivea and Simple patches also developed a violet-purple hue, although noticeably lighter. There was, however, one standout. The sticker coated in La Roche-Posay Anthelios remained completely transparent. Seeing such a clear difference between patches reassured me that the stickers were certainly reacting differently, depending on what was sitting on top of them. But the biggest surprise came when I looked at my other arm. Nivea Protect & Moisture SPF50 200ml, £6.89 Credit: screengrab Simple Hydrating UV Fluid SPF50 40ml, £6.49 Credit: screengrab The Superdrug and Boots patches had both turned a deep purple, while the Supergoop! sticker had taken on a lighter violet shade. Yet the clearest patch of all was covered by the cheapest sunscreen in the entire test: Aldi Lacura SPF50+. Considering it cost £43 less than the Trinny London formula, I was rather baffled. Aldi’s formula contains five different UV filters, as does the Trinny London cream. As a two-in-one moisturiser and SPF, the latter also contains a host of skincare ingredients designed to hydrate and condition the skin. Aldi Lacura SPF50+ 50ml, £2.80 Credit: Unknown Supergoop! Unseen Sunscreen SPF50+ 50ml, £36.50 Credit: screengrab In other words, there was no obvious explanation why Aldi’s bargain formula should have had the upper hand. I wondered if the stickers, which thousands of sun-worshippers are using to gauge how much sunscreen to slap on, were as reliable as they’d have us believe. “UV detection stickers are a clever visual tool and, depending on the product, potentially prompt you when it may be time to reapply,” says Dr Ahmed El Muntasar, owner of The Aesthetics Doctor. “But they are not a substitute for proper SPF testing and I certainly wouldn’t conclude that one sunscreen is better than another simply because of how a sticker reacts. Superdrug B.Skincare SPF50 Moisturiser 75ml, £10 Credit: Screengrab SPF+ Hyaluronic Acid Moisturising Lotion SPF50 50ml, £8 Credit: screengrab “A small colour-changing sticker simply cannot reproduce that level of testing or tell you the complete protective profile of a sunscreen.” Dr Ahmed points out that it also depends on “how much sunscreen has been applied, how evenly it has been spread, how long it has been allowed to dry, and the intensity of UV exposure.” He adds, “Even the way different formulations sit on the sticker can potentially influence what you see.” If there is some truth in the results, however, they reinforced the biggest surprise of my experiment – that spending more didn’t mean the UV sticker would stay clearer for longer. Because after being in the sun for over two hours, most of the stickers had turned purple except for La Roche-Posay, which was still clear. And even if these patches are no substitute for proper SPF testing, they did at least make me more conscious of my sunscreen levels once out in the sun. Dr Ahmed says: “I actually think the stickers’ best use is behavioural rather than diagnostic. “If seeing the colour change reminds somebody to apply enough and reapply regularly, that’s potentially very useful. “There is research suggesting UV detection stickers can increase sunscreen reapplication, but consumers shouldn’t disregard a properly tested product because of the result of a home sticker experiment.” For me, the lessons were threefold: don’t assume an expensive SPF is automatically doing a better job, don’t skimp when applying it and, most importantly, always remember to reapply.