Constantly re-applying sun cream when you're out and about can be a real chore, especially if you're trying to keep wriggly kids protected.
So it's not surprising that brands have sought to make life easier for us by developing hard wearing sun creams.
Boots Soltan Kids Once, Calypso Once a Day and Riemann P20 Once a Day are among the brands we've found claiming to offer all day protection.
They tend to be more expensive than standard sunscreen and claim to offer high and long lasting protection, usually by forming a more resistant film on the skin than standard sun cream.
But do 'once a day' sunscreens really last all day? And should you rely on them? Our research, and the small print on the bottle, suggests you may need to re-apply more often than you think.
Applying sun cream just once before getting on with your day sounds really tempting.
But take a look at the small print on the back of the bottle, and it becomes clear that these all day protection claims come with a list of crucial caveats.
Sweating, swimming, towel drying, or rubbing your skin on an abrasive surface can all impact protection levels and how the sunscreen lasts. All of this means you’ll almost certainly need to apply more than just ‘once a day’, especially if you're out and about.
Brands aren’t allowed to make 'once a day' claims on sunscreen in Australia, due to concerns they give people a false sense of security, but there's no such restriction in the UK. We've raised concerns about this before, and it's disappointing to see leading brands still pushing family versions of these products.
The Once 'Advanced Protect' range costs around £10 for a regular sized bottle - more than double the price of its £4 Soltan ‘Protect and Moisturise’ range, which Boots says should be reapplied every 1-2 hours.
The small print:
Back of pack instructions say you need to apply the sun cream generously 15 minutes before sun exposure and re-apply after towel drying or 'coming into contact with an abrasive surface'.
We asked Boots what counts as an abrasive surface and it said rubbing wet skin with a towel would count but that sunbathing on an abrasive surface (such as a towel, the sand, or a sunbed) would not. We question whether the packaging info is clear enough for users.
The small print:
Calypso says 'one correct application' will 'help to protect your skin all day long'.
On its website, it says you need to reapply after 40 minutes in the water, if you dry yourself with a towel, or after ‘anything that involves rubbing your skin.’
The small print:
Riemann says the product should be reapplied after 'excessive sweating or after towel drying.'
Riemann told us it has phased out the term 'once a day' in recent years, so any packs you do see with this branding are leftover stock. Instead, new packs use the word 'durable'.
However, the above caveats still apply to the 10 hour durability claim.
It's clear that there are plenty of conditions to fulfil to get the claimed protection from once-a-day products, which may be hard to achieve if you're on a day out in the sun.
What's more, even if you follow all the rules, it's possible you won't get as much as protection as you expect.
In 2016 Which? put several once-a-day sunscreens to the test, investigating how long they lasted on volunteers in a controlled lab experiment, and found they didn't offer nearly as much protection as claimed.
We tested products from Boots Soltan Once, Piz Buin and Riemann at the time, which were applied to the backs of volunteers who then spent the day in the lab.
They were allowed to wear t-shirts and sit on a chair (we did this because if you lie on a sun lounger or towel, get sandy, or wear a t-shirt on holiday it’s possible your single-use sunscreen could be rubbed off over time).
After several hours we retested each sunscreen’s SPF and saw a shocking 74% average decrease in protection.
At the time, the Cosmetic, Toiletry and Perfumery Association (CTPA) criticised our use of t-shirts. But we stand by our testing, which we think reflects real-life use. We're concerned that ‘once a day’ claims are still being made in 2022, despite the CTPA since encouraging brands to move away from such wording.
The British Association of Dermatologists (BAD) says frequent reapplication of sun cream is important, regardless of how long any product claims to give protection for.
Professor Brian Diffey, of BAD, says: 'We recommend against relying on any sunscreen product for long periods without reapplication, whether advertised as an extended wear product, or not.
'Nobody applies sunscreen perfectly uniformly to all exposed skin and it is inevitable that we will miss patches of skin.
‘So, if you are only applying your sunscreen once a day, you are at risk of spending hours in the sun with little or no protection to those areas of skin that may have been missed.'
Over the course of a day, he added, 'swimming, drying, sweating, getting dressed and undressed' can cause sun cream to be wiped or washed away.
'People can still use these types of sunscreens, but you should treat them like any other sunscreen, and reapply regularly,' he said.
Since our 2016 investigation, the CTPA has advised brands to voluntarily stop making 'once a day' claims and move towards using the word 'durable' instead.
But while some brands - including Piz Buin and Riemann - have phased out the use of 'once a day' on packaging in the UK, others, such as Boots, have not.
The CTPA told us long lasting sun creams have a legitimate place in the market, and that brands must have robust and in-depth research to back up any claims.
But it also acknowledges the importance of making sure the message of frequent re-application is clear, which is why it recommends members move away from 'once a day' descriptors.
A spokesperson added: 'As with all sunscreens, it is important to follow the instructions for application and use; and sunscreen should not be used to intentionally stay longer in the sun. Sunscreen is just one part of a sun safe regime.'
We asked Boots a series of questions about its Once sun cream range and asked it to respond to our concerns about 'once a day' claims.
A spokesperson said: 'Soltan Once products clearly state how they should be used and when to reapply. We are confident in the claims for the Soltan Once range and refute the suggestion that they are misleading.
'Casting incorrect assertions in this manner is misleading and confusing to customers and we are disappointed that Which? has chosen to do this.'
We made multiple attempts to get in touch with Calypso, but the brand did not respond to any of our questions or send us a comment.
Riemann told us that it has already phased out the use of 'once a day' claims on its packaging and that any stock still showing online or in-store are leftover products.
A spokesperson told us that all of its sun creams are designed for 'longevity' but that it found the use of the word 'durable' more 'appropriate' than once a day.
This is because, she said, the length of protection can vary depending on a person's activities - including how much they sweat and whether they towel dry, for example.
The use of the word durable, she added, aims to communicate its long lasting characteristics without 'promising [a] full day protection guarantee, with no need for reapplication.'
'We agree that the claim “Once a day” can be anticipated in a wrong way by the consumer, and it is one of the reasons why we changed our durability communication from “Once a day” to “Up to 10 hours”.
The British Association of Dermatologists says when using lotions, you should aim to apply at least six full teaspoons to cover the body of an average adult and should apply it at least 15 minutes before heading out in the sun so it can sink in.
The association estimates most of us only apply half of this amount, which means we're often less protected than we think we are.
Professor Brian Diffey recommends applying sun cream like you would paint to a wall - you'd rarely just do one coat. Two coats of paint are almost always required for satisfactory coverage. In the same way two coats of sunscreen may be required for adequate protection,' he said.
And after that, he adds, re-apply at least every two hours - and immediately after swimming, sweating or towel drying.
Yes, you can - but you’ll also need to reapply frequently, just like you would if you were on the beach staying dry, and immediately after towel drying.
Professor Brian Diffey adds that sun creams generally offer ‘very good’ water resistance these days (though be aware water resistance claims also come with caveats, and the products we tested didn't hold up well to real-life conditions in our 2016 investigation), which is good if you're planning on spending time in the pool or in the sea. But over the course of the day swimming will wash away some of the protection.
‘The regular reapplication advocated by most sunscreens protects us against this,’ he says.
Don't just rely on sunscreen either: use clothing, hats, sunglasses to cover up, and seek shade, particularly when the sun is strongest, between 11am and 3pm - regardless of whether you are wearing sun cream.
Prices correct as of 28 July 2022, based on the SPF 30 version of each brand's Once a Day range.