Sun protection is getting more complex. One of the hot areas of sun protection research these days is in UVA – what is it and why should you be worried?
What is UVA?
As you no doubt know, the sun emits UV radiation, along with heat and visible light. UV can be divided into 3 types, according to their energy, which is inversely proportional to wavelength (in other words, short wavelength = more energy):
UVC (wavelengths 100-280 nm) – This is the most harmful, but also the least penetrating. It’s almost completely blocked by the atmosphere and the ozone layer, so we don’t need to worry too much about it.
UVB (wavelength 280-315 nm) – This is the one that you’ve probably heard about the most. About 90% of UVB from the sun is absorbed by the ozone layer, which means for Australians it’s a bigger issue since we’re near the ozone hole and we have excellent sunny weather. It causes sunburns and skin cancer, but is mostly blocked by glass. It’s also the type of UV light that’s involved in the production of vitamin D in the skin. UVB is strongest in summer, and in the middle of the day.
UVA (wavelength 315-400 nm) – UVA penetrates the atmosphere better (it’s ~95% of UV radiation reaching Earth), and it also penetrates deeper into your skin than UVB. It forms highly reactive free radicals in the skin, which randomly react with whatever’s around (your DNA, for example), causing wrinkles and old-looking skin, as well as deadly melanomas. It’s the type of UV light that’s used in tanning beds and black lights. Like UVB, UVA levels vary depending on the time of day and the season, though it varies a lot less, so it’s important to think about UVA protection at off-peak times as well.
The reason UVA is less famous than UVB is that the dangers of UVA weren’t known until recently. The effects of UVA are also less immediate and build up over time, which makes them more dangerous. UVA’s penetrative power is also scary – it can penetrate through glass, like the glass in your car’s side windows, which is why there are lots of asymmetric skin cancer and wrinkle patterns emerging, such as on this veteran truck driver.
|New England Journal of Medicine|
Even if you never go to the beach or lie in the sun, you’ll still be affected – it’s been estimated that 80% of UVA damage comes from everyday exposure, during activities like walking, driving and even sitting near windows.
Sunscreens and UVB
Sunscreens are almost always labelled with an SPF (Sun Protection Factor). This was introduced during the 1970s, before all the UVA-is-dangerous research, when it was assumed that UVB was the only type of UV to be concerned about.
SPF only tells you how much UVB protection (mostly) a sunscreen gives you, and very little information about UVA. Specifically, the SPF tells you how much longer it takes for your skin to burn with the sunscreen on, compared to without. For example, if your unprotected skin burns in 10 minutes with a particular UV intensity, an SPF 30 sunscreen (applied correctly, and assuming it’s photostable) would protect you from burning until after 300 minutes of that UV intensity. SPF numbers are determined by testing each sunscreen in a laboratory – sunscreens containing the same amounts of the same active ingredients don’t necessarily have the same SPF value. Since burning is mostly (80-90%) due to UVB with the rest due to shorter wavelength UVA, protection against the longer wavelengths of UVA isn’t really measured.
Sunscreens and UVA
In Australia and many other countries, there’s no standard measurement for exactly how much UVA protection you’re getting from a sunscreen. However, there are regulations around the term “broad spectrum” – in many parts of the world (including Australia), to label a sunscreen “broad spectrum”, the UVA protection must be at least 1/3 of the SPF value. In Australia, all sunscreens with SPF 30 or higher must be broad spectrum. For better UVA protection, it’s best to choose a broad spectrum sunscreen with as high an SPF possible.
In some Asian and European countries, there are numerical ratings for UVA, although there’s no one standard yet. The most common are:
PPD – This stands for “persistent pigment darkening” and measures how protective a sunscreen is against a long-term tan caused by UVA – it’s essentially the equivalent of SPF for UVA radiation. It’s commonly used for European sunscreens. PPD 10 blocks about 90% of UVA rays, and is generally considered to be suitable for everyday use. For some reason PPD values are usually hidden away on the sides of packaging.
PA – This is a similar concept to PPD, but rates sunscreens on their UVA protection with plus signs (+). It’s more popular in Asian countries. PA+ is roughly equivalent to PPD 2-4, PA++ is PPD 4-8, PA+++ is PPD 8-16 and PA++++ is PPD 16 and above. (If you’re mathsy, the conversion is 2number of plus signs.) Many Asian sunscreens have PA ratings prominently listed.
The most effective UVA-protective sunscreen ingredients around at the moment are avobenzone, ecamsule (Mexoryl SX), bemotrizinol (Tinosorb S), bisoctrizole (Tinosorb M) and zinc oxide. Oxybenzone, dioxybenzone, octocrylene and titanium dioxide are less effective but still block some UVA wavelengths.
As you can probably guess by now, sunscreens aren’t the best sun protection – many don’t have complete UVA protection, they need reapplying, and it’s really easy to miss a spot or apply too little. Luckily, there are other options:
- Wear sun protective clothing, hats and sunglasses. Hats are especially good for protecting your scalp – I know I never put sunscreen on my scalp!
- Seek shade and avoid sun exposure at peak times. Reflected UV will still cause damage, but less than direct UV.
- Add UVA tints to windows that you go near frequently, such as at home or in your car. Many windshields are already designed to block UVA.
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Last updated: December 29, 2017 at 18:21 pm