Chemical sunscreens work by absorbing the sun's rays and physical sunscreens work by deflecting or blocking the rays from your skin. Many sunscreens combine a mixture of chemical and physical blockers.
Mineral sunscreens are comprised of physical blockers such as titanium dioxide and zinc oxide, which tend to offer a wider spectrum of UV protection and are deemed safer because they don't absorb into your skin like chemical blockers and are less likely to cause allergic reactions or skin irritations. Unfortunately physical blockers can leave an unsightly sheen on your skin - think Shane Warne in his baggy greens, pre-Liz Hurley.
More recently, nanotechnology has enabled the creation of ultra fine particles of zinc oxide and titanium dioxide, resulting in clearer sunscreen formulations. Good news, right? Maybe not. Although research is inconclusive, concerns have been raised over the use of nanoparticles in sunscreen and other cosmetics.
In July this year, New Zealand's Environmental Protection Authority (EPA) announced an amendment to labelling standards for cosmetic products, including sunscreens. By 2015, products will have to list nano-scale ingredients on their labels and highlight the ingredient by placing 'nano' next to it in brackets.
THE SLIPPERY TRUTH
While some sunscreens boldly state to be waterproof, the argument isn't a watertight one. Sunscreens contain an emulsifier to help ingredients mix, but because emulsifiers act as detergents, once in contact with pool water or the ocean, they can dissolve the sunscreen on your skin. In July this year, Australian/New Zealand Standard released a revised standard for sunscreens that no longer permits the use of the terms 'waterproof' and 'sweat proof' on sunscreens because they are both misleading.
WHAT TO AVOID
Oxybenzone is a synthetic estrogen which has been linked to hormone disruption and when exposed to sunlight, creates harmful free radicals that destroy or inhibit the skins natural defences against sunlight.
Retinyl palmitate is a type of vitamin A commonly found in sunscreens. A joint report by the US Environmental Protection Authority and the National Toxicology Program concluded that retinyl palmitate led to the early onset and larger amount of skin lesions and squamous (cancerous) cell tumours.
Parabens are preservatives commonly found in sunscreen and a range of cosmetics. Some evidence suggests parabens can mimic estrogen and in some cases they've been found in breast cancer tumours.
Fragranced sunscreens contain a high amount of chemicals that can trigger asthma and, like parabens, some have been shown to mimic estrogen and make breast cancer cells grow in laboratory studies.
Expired sunscreens are likely to have lost some of their effectiveness. Use-by dates are determined by how long the sunscreen will retain its efficacy and safety, which is typically anywhere up to three years.
WHAT TO LOOK FOR
Keep an eye out for zinc, titanium, avobenzone or Mexoryl SX on the ingredients label. These substances remain largely on the skin, protecting it from both UVB and UVA radiation. However, it's worth remembering that the use of zinc nanoparticles in sunscreens remains a contentious issue, although EWG maintains that many zinc and titanium-based sunscreens are among the safest and most effective sunscreens on the market.
Broad Spectrum
Look for sunscreens that offer protection against both UVA and UVB lights. Products carrying the term 'broad spectrum' are your best bet.
