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. Avoid sun exposure between 11am - 3pm. Seek shade and always protect children with a hat, loose clothing and high SPF protection. Reapply sunscreen after swimming, sweating heavily, towel drying, or rubbing your skin in a way that might cause the cream to rub off. Mineral sunscreens fail Which? SPF and UVA tests - find out what happened when we put pricey mineral formulations to the test in our independent lab

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.' Calypso 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.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.' Boots

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”.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. 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. 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. Important: Read the instructions carefully before use. Apply to clean dry skin, preferably after a shower. Apply evenly and generously 15 minutes before exposure to the sun, which will allow the product to bind with the skin and form a protective film against UVA/UVB rays. When used correctly, one application is sufficient for all day protection. 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.