What is ultraviolet radiation and what is UVA? Why do we need to block it and how can you tell if your sunscreen does a good job? These are important questions but not ones easily answered by the average consumer. The following is a brief explanation of UVA, its importance to you, and what to look for in an effective sunscreen.
UVR and Traditional Sunscreens
The sun emits a number of different types of radiation, including ultraviolet radiation (UVR). UVR is divided into three types: UVA, UVB and UVC, each of which reflect different wavelengths. Radiation exists as waves--much the same as ocean waves, in fact. The wavelength is simply the distance between the tops of two consecutive waves.
UVC rays are completely filtered out by the earth's atmosphere so they don't reach us. UVB rays, however, are only partially blocked by the atmosphere, so some does get to us. These are the rays that cause sunburn and some types of skin cancer. Since sunscreens have traditionally been designed to stop sunburn, it is the UVB rays that they normally block. The SPF number of a sunscreen is an indication of how much UVB a sunscreen will block. An SPF 2 will block 50% of the UVB rays so you can stay in the sun twice as long without burning as you would have been able to without the sunscreen. With an SPF 15, 93% of the UVB rays are blocked and you can stay out 15 times as long.
There are a couple of very important things to keep in mind: (1) The SPF number assumes the sunscreen was applied before exposure. If you apply the sunscreen after being exposed to the sun, the number no longer applies. (2) Also, if you stay out longer than the SPF claims to protect for, you will still be burned. As an example, if you would normally burn in 10 minutes and you put on an SPF 2 before you go out, it will take 20 minutes before to burn. Sunscreens do not provide total protection; they simply lower the amount of UVB that gets to you. It's analogous to standing behind a screen. The screen blocks only some of the light but some continues to get through, so if you stand there long enough eventually you will get burned.
UVA is divided into two parts, long UVA and short UVA. For all intents and purposes, short UVA behaves very much like UVB. It can cause sunburn and is at least partially blocked by most sunscreens. Long UVA, however, does not cause sunburn. In fact it does not cause any sort of immediate reaction, even in pretty large doses. The SPF number provides no information about a sunscreen's UVA blocking capabilities. Unfortunately, even the words "broad spectrum" don't tell you much about the amount, if any, of long wave UVA protection. Current law allows the labeling of sunscreens with the words "broad spectrum" and "protects against UVA" when they only block short UVA. There is no legal requirement to block long UVA and, in fact, the vast majority of sunscreens on the market do not.
Why Bother to Block UVA
It turns out that long UVA can cause the skin to age and is likely involved in the more serious skin cancers such as melanoma. Wrinkles, uneven pigmentation, sagging and age spots associated with old age are mostly due to sun exposure and could be prevented with sun avoidance, proper clothing and a good sunscreen that blocks long UVA. It has been suggested that sunscreens that block only UVB and some short UVA might be doing damage because they allow one to be exposed to larger amounts of long UVA than the person otherwise would have been. This remains a controversial point, but few will argue that long UVA should be blocked.
Choosing a Sunscreen
As mentioned above, there is no label requirement for long UVA. The American Academy of Dermatology has made recommendations to the FDA regarding this, yet no law has been enacted. At last notice from the FDA, it looks as though no long UVA labeling will be required until at least 2005. What is the consumer supposed to do until then?
The only answer is to read the label and question your sunscreen manufacturer. There are a number of ingredients that block long UVA including zinc oxide and avobenzone, otherwise known as Parsol 1789. Although avobenzone blocks long UVA, it has some issues that limit its usefulness. Avobenzone is photo-unstable, meaning that it breaks down in the sun and there is clinical evidence that it can cause allergic reactions.
Zinc oxide is very photo-stable and is not known to cause any allergic reactions. Early versions of zinc oxide were white and pasty. Newer versions are completely transparent and very elegant.
Whatever sunscreen you chose, make sure it blocks UVA and ask the manufacturer about what tests they conduct to insure this – its your skin and you need to take control of how you treat it.
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