Latest Fact Sheet

Season 3, Ep 6 - Sun Screen

· There are three types of ultraviolet (UV) radiation emitted from the sun – UVC is absorbed by the ozone layer – only UVA and UVB rays reach the Earth’s surface.

· UVB rays can penetrate the top layer of the skin and can damage DNA. UVB causes sunburn.

· UVA rays are able to penetrate further into the skin than UVB. UVA is responsible for phtoageing – the wrinkling of skin associated with sun exposure.

· UVB rays are partially filtered out by the ozone layer. UVA rays can penetrate both clouds and glass.

· Both UVA and UVB rays are implicated in the development of skin cancers. UVB directly damages DNA, while UVA produces free radicals that can indirectly cause cancer by damaging DNA or impairing the processes that repair damaged DNA.

· Sunscreens fall into two types – physical blockers reflect UV rays while chemical absorbers absorb the rays. Chemical absorbers only absorb certain wavelengths so different types are used in conjunction to provide protection against UVA and UVB.

· Sun Protection Factor (SPF) gives an indicator of how many times longer it will take for skin to begin to burn while wearing the sunscreen as opposed to bare skin. For example, if skin takes 10 minutes to burn without sunscreen and 100 minutes with a sunscreen then that sunscreen has an SPF of 10.

· But because UV intensity changes during the day, so does the time it takes to get a sunburn. It might take an hour to get burnt at 10am, but just a few minutes at noon.

· SPF is only a measure of protection against UVB (which causes sunburn), it doesn’t provide a measure of protection against UVA.

· SPFs as high as 80 and 90 exist but these can encourage complacency in sunscreen use – not only does the SPF not provide the same protection against UVA, over time sunscreens are likely to be damaged by the sun which renders them ineffective. Over time sunscreen also gets rubbed and sweated off. It’s important to reapply sunscreen every two hours.

· There are so many problems with the SPF rating that the American FDA has considered doing away with it altogether. In the end they have opted to rename it as the less misleading Sunburn Protection Factor. The new rules are due out in October.

· Even sunscreens that are labelled as being ‘water-proof’ or ‘water-resistant’ will probably wash off when you are swimming. It’s a good idea to reapply sunscreen after swimming. Part of the problem is that sunscreens are oil and water emulsions – so they contain an emulsifier to help the ingredients mix. Emulsifiers are basicaly detergents, so they can also help the sunscreen on your skin dissolve in seas or swimmingpool water.

· When looking out for a sunscreen look for products that contain both a physical blocker such as titanium dioxide or zinc oxide as well as a chemical absorber – benzophenone. This type of sunscreen is most able to protect the skin from both UVA and UVB rays.

· When using sunscreen it’s important to use enough – around seven teaspoons. That’s one teaspoon for the face, neck & shoulders; one for each arm; one for each leg; one for the back and one for the chest and stomach.

· It takes 20-30 minutes for sunscreen to be absorbed so it’s important to put it on at least 20-30 minutes before going out in the sun.

· Nanotechnology is used by some sunscreen manufacturers to make physical blockers smaller. This means that although they still reflect UV light they aren’t visible on the skin – normal sized physical blockers leave a white-ish film on the skin.

· There is concern that nano-sized ingredients in sunscreen could penetrate the skin however at present the evidence suggests that this is unlikely.

· Sunscreen can go off – if sunscreen has a strange consistency, is partially crystalised or separates then it’s likely to be ineffective and needs replacing.

· The highest UV intensities in New Zealand are 40% higher than those at comparable latitudes in the northern hemisphere. This is thought to be due to New Zealand having less ozone, the earth being closer to the sun in the southern hemisphere summer than it is in the northern hemisphere summer and the cleaner air found in New Zealand.