It's common for sun creams to claim to be 'water resistant', but this doesn't mean that they're waterproof. Even with our test subjects just sitting on a chair in a T-shirt, we saw substantial reductions in the level of sun protection, so we don't think you can rely on once-a-day sun cream to keep you protected all day.

We award Which? Best Buy status to products that we've independently reviewed that meet all our tough criteria: they must pass independent lab tests for UVA and UVB sun protection, and be easy and pleasant to apply.Avoid sun exposure between 11am - 3pm. Seek shade and always protect children with a hat, loose clothing and high SPF protection.

Some people worry that using sun cream might prevent them from getting enough vitamin D, but this isn’t the case unless you really overdo it. Physical/mineral products reflect visible light as well as UV, which can make the formulations opaque and leave a white residue on the skin. Some formulations use nanoparticles of titanium dioxide and zinc oxide – the minerals responsible for the residue. Nanoparticles are smaller, and as they scatter visible light – rather than reflect it – the sun creams are transparent. How to use sun cream Mineral sunscreens in particular often promote their environmental credentials, the most common being that they’re ‘reef-safe’ or 'ocean-friendly'. Physical or mineral sun creams create a barrier on the skin that acts like a mirror, reflecting and scattering the UV light. This tends to mean that two commonly used chemical UV filters linked to coral bleaching – oxybenzone and octinoxate – aren’t used.For reasons of hygiene and safety, personal grooming products, cosmetics or items of intimate clothing cannot be returned.

Apply evenly and generously, smooth in gently. We recommend a minimum quantity of 35ml for all over body protection. Find out what you need to know about 'once a day' sun creams, water-resistant sun creams, sensitive sun screen and the best kids' sun cream too.

The industry guideline for water-resistant sun creams allows the SPF of a product to drop by 50% after a total of 40 minutes in water. Water-resistance testing also takes place in what is essentially a bath – using tap water. You can buy sun cream in pharmacies, supermarkets and discount stores, with some of our tested options coming from Asda, Boots, Garnier, Nivea and Wilko. Remember, sun cream is just one part of staying safe in the sun and it's also really important to encourage kids (and adults) to:

If you're using sun cream at the beach, apply plenty before swimming, and again when you leave the water. Reef-safe sun creams Babies less than six months old should be kept out of direct sunlight, according to the NHS, and the skin of young children should be protected from the sun when UV levels are high. We saw an average 74% decrease in SPF protection at the end of the tests. We shared our concerns with Cancer Research UK (CRUK) and the British Association of Dermatologists (BAD). Both advise against relying on any sun cream for extended periods in the sun.Always be aware of the strength of the sun. Never exceed sun exposure for longer than your skin allows. Remember - all skin types are different.