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. For reasons of hygiene and safety, personal grooming products, cosmetics or items of intimate clothing cannot be returned. It's common for sun creams to claim to be 'water resistant', but this doesn't mean that they're waterproof. Oxybenzoneis another ingredient to avoid as it is easily absorbed by the skin and enters the bloodstream, and it can disrupt your hormones as well as causing terrible harm to the environment. Physical or mineral sun creams create a barrier on the skin that acts like a mirror, reflecting and scattering the UV light.

Water resistance: For a sun cream to be water resistant, it must have undergone testing to show that it stays effective for at least 40 minutes in the water. After this time, you will need to reapply. Sun cream provides protection from sunlight using UV filters. These are classified into two types: chemical and physical – also known as mineral sun cream.He added, "Most people apply sunscreen too thinly and that means protection is reduced. An adult should be applying around six to eight teaspoons to cover their body. We tested two popular sun creams in chlorinated water (to mimic a swimming pool) and salty water (to emulate the sea). We also added another scenario using fast-moving tap water to see what effect this had. Most of the time, the products weren't as effective in our more realistic conditions as they were in tap water. 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. Consider the time of day – If you're spending time in the sun without wearing sun cream, you should only do so before 11am or after 3pm, as the middle of the day is when you're at the greatest risk of getting burnt.

Dr Paul Banwell told us, "Some sunscreens use chemicals, such as oxybenzone, a known- allergen, and avobenzone to absorb UV rays, which can be detected in the body at harmful levels." Mineral sunscreens in particular often promote their environmental credentials, the most common being that they’re ‘reef-safe’ or 'ocean-friendly'. 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 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. If you're someone who's in and out of the pool or sea when the sun comes out, then this formula from Bondi Sands might be the one for you. It's specially formulated to be water resistant for four hours - far longer than the 40 minute criteria that other water resistant sun creams must meet. It's infused with ethically sourced algae for deep hydration and is, of course, reef friendly too.

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Eat well, live better and stay healthy - sign up for our free monthly Food & Health newsletter for the latest insights delivered straight to your inbox The NHS recommends reapplying sun cream every two hours, as the sun can dry it off your skin. They add that when applying sun cream for the first time that day you should do this twice: 30 minutes before going out and again just before leaving. If you're using sun cream at the beach, apply plenty before swimming, and again when you leave the water. Reef-safe sun creams

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. It's always best to choose sun creams that have an SPF of 30 or above, and a UV star rating of at least four stars, as these will protect you best. In addition, some sun creams contain chemicals that some people may find irritating or cause a reaction on their skin. For any product to provide the SPF it claims, you need to apply 2mg per square cm – which means around a teaspoonful of product for your face. And, just as with sun cream, it needs to be reapplied regularly. For more details on the importance of vitamin D and where to buy supplements, see our in-depth vitamin D guide . Other ways to stay safe in the sun Cover up – wear sunglasses to protect your eyes and grab a hat if you need to keep your face out of the sun. You might also want to wear a T-shirt, which can help to cover up typically over-exposed areas such as shoulders.

For environmentally conscious sun-seekers, this sun cream by Forever Living is the one to go for. It won the best sunscreen category in the Green Parent Beauty Awards in 2021, and it's vegan and cruelty-free. The inclusion of aloe vera and vitamin E is extra moisturising and soothes the skin, and the formula promises to be water resistant for 80 minutes. 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. It takes longer for those with darker skin that rarely burns – it can take 25-40 minutes for the darkest skin type. Dermatologist and cosmetologistDr Eva Melegh told us: "If you are prone to sensitive skin or you are applying suncream to children’s skin then you it’s best to opt for mineral sun creams as opposed to chemical filter ones, as they have less chance of causing a skin reaction to sensitive skin. If you have sensitive skin a very helpful product is Kalme Undercoatwhich is designed to wear under sun creams to reduce the risk of skin reactions." From April to September, when the UV Index is generally higher. It takes 10 to 15 minutes of sun exposure each day for those with fair-to-olive skin to get enough vitamin D.

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. This tends to mean that two commonly used chemical UV filters linked to coral bleaching – oxybenzone and octinoxate – aren’t used. He added, "Other ingredients that may cause reactions include benzophenones, cinnamates and dibenzoylmethane.

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: I would avoidOctinoxate,which is harmful to coral reefs and can cause skin allergies as well asAvobenzone,which can cause high levels of irritation. You also need to avoid Retinyl Palmitate, which does not mix well with the sun. When mixed with the sun, it can be potentially cancerous." When choosing sun cream for your child, look for a short ingredients list and the terms 'fragrance free' and 'hypoallergenic'. The WHO recommends 35ml of sun cream (seven teaspoons' worth) to cover an adult, so use around a quarter to a half of this depending on the size of your child.