Are you diligent about slathering on sunscreen before heading outdoors? Good job. You've taken a huge step in reducing your chances of getting all types of skin cancer by protecting yourself from harmful ultraviolet radiation. The not-so-good news: four in five sun protection products offer "inferior sun protection or contain worrisome ingredients", according to a new report by a non-profit environmental research organisation in the US. The Environmental Working Group (EWG), based in Washington, reviewed more than 1,700 products such as sunscreens, lip balms and moisturisers that boast a sun protection factor, or SPF, which refers to protection against sunburn-causing UVB rays. In its report released two weeks ago, the group highlights two chemicals - oxybenzone, which can disrupt the hormone system, and retinyl palmitate, a form of vitamin A that is linked with skin damage. Other dangers flagged include spray-on sunscreens, which they say may not be safe or effective, and SPF values over 50+, because SPF allegedly tops out at 30 to 50. "EWG's Sunscreen Guide for 2015 - the 9th annual edition - finds persistent problems with the ingredients and marketing of sunscreens for the American market," reads the report. EWG estimates more than half of the sunscreens on the American market would not make it to stores in Europe. Among the brands in its "Hall of Shame" - products that they claim "promise safe sun protection and don't deliver" - are Neutrogena, Banana Boat, and Coppertone. These brands are commonly found in Hong Kong on supermarket shelves and in personal care stores such as Watson's and Mannings. Overall, 217 products reviewed meet EWG's criteria, achieving a rating of 1 or 2 on a scale of 10. View the results at ewg.org/2015sunscreen to see if the sun product you're using makes the cut - or look for one that does. Products are rated on five factors encompassing overall ingredient safety and product efficacy in providing sun protection. These include UVA and UVB protection, sunscreen stability, and health hazards associated with listed ingredients based on a review of nearly 60 standard industry, academic, government regulatory and toxicity databases. Some skincare manufacturers and dermatologists, however, have alleged EWG's annual review lacks scientific rigour, with an arbitrary rating system not based on any accepted scientific standard. Critics also say some of the best sunscreens on the market - not reviewed by EWG - have newer chemicals that are much more effective. Further, there is no scientific consensus to the "worrisome ingredients" such as oxybenzone and retinyl palmitate flagged by the group. Oxybenzone is a synthetic oestrogen approved for use in sunscreens by the US Food and Drug Administration in 1978 to provide effective broad-spectrum protection from UV radiation from six months of age onwards. According to the US Skin Cancer Foundation, some studies have showed that it can penetrate skin, interfering with hormone levels. It can also trigger allergic skin reactions. However the foundation did its own research review and found no basis for concern about the use of sunscreens containing oxybenzone. The foundation says the studies were conducted on rats and "no evidence has shown that oxybenzone has any adverse health effect in humans". Although the chemical is absorbed by the body, it is excreted and does not accumulate. The same goes for retinyl palmitate. "There is no scientific evidence that retinyl palmitate causes cancer in humans," says the foundation. Several studies suggest that, when exposed to UV radiation, retinyl palmitate generates free radicals - chemically reactive substances whose interactions with DNA may cause mutations leading to cancer. However, the foundation says these studies have examined retinyl palmitate only as it reacts to UV radiation in isolation. In practice, antioxidants such as vitamins C and E present in the body can neutralise it. In fact, retinoids, (topical vitamin A products similar to retinyl palmitate) are commonly prescribed by dermatologists, and used in lotions and night creams. Their oral form is often prescribed to prevent skin cancers in people at high risk of the disease. Regulation of sunscreens vary among countries. The US and European Union, for example, have different lists of approved chemicals for use in sunscreens. And while the European Commission, Japan and Australia have barred SPF ratings above 50+, the US hasn't. In Hong Kong, there are no regulations for bringing sunscreen to market or limits on maximum SPF ratings. The Hong Kong CancerFund advises that a properly applied SPF 30 to 50 sunscreen will block about 97 per cent to 98 per cent of UVB rays. Without sunscreen, it takes 20 minutes for your skin to burn, so, theoretically, using an SPF 15 sunscreen means it will take 15 times longer to burn - or about five hours. An SPF of 30 will theoretically prevent your skin from burning for 10 hours. An SPF of 100 is not twice as good as 50; no sunscreen offers 100 per cent protection. Proper and repeated application of sunscreen every two hours is more important. Ensure the sunscreen also has appropriate protection against UVA, which penetrates deeper into the skin than UVB and causes more long-term damage, such as pigmentation, wrinkles and premature skin ageing. The CancerFund recommends checking the product label for one of these statements: "broad spectrum UVA/UVB", a UVA logo within a circle, or a PA++++ rating. On an average-sized adult, a teaspoon of sunscreen should be applied per major body part, or a total of about 35ml for the entire body.