UV ABCs

It's summertime and the living is easy...

Y'all know the sunlight skin damage basics, right? Let me sum up:

1. It's the UV (ultraviolet) rays from the sun that do all the damage — from wrinkles and leathering to cancer. There are three types of UV rays (UVA, UVB and UVC), but for the foreseeable future, we really only have to worry about two of them.

2. UVB rays cause mostly superficial sun damage to your skin, as in sunburns, but are also responsible for skin cancer, particularly melanoma. Because, I imagine, UVB causes immediately visible damage, these are the rays that have been the focus of sunscreen since the 60s. UVB light is also weather and season dependent — the rays are absorbed by clouds and rain, diffusing their impact on your skin, and they are stronger the closer you are to the sun (e.g., depending on the season or the latitude of your location).

3. UVA rays, it turns out, are the real monster in the sky. These baddies don't care if it's July 4th or Christmas, and a little bit of window glass isn't going to slow them down a bit. Which is a real shame, because UVA light is responsible for the really bad things, like tanning, wrinkles and causing and accelerating skin cancer. UVA rays penetrate the epidermis (skin's top layer) to the dermis (skin's middle layer) below.

It's kinda like this: the epidermis is the grass and the dermis is the sod. The epidermis, layers of living cells topped by layers of dead cells, is what you see, and it can look lush, pretty and green or tired, brown and dry, depending on what's going on underneath. The dermis, entirely made up of living cells and blood vessels, is responsible for the firmness, elasticity, and strength of your skin.

Okay, yes, I said tanning as though it's a bad thing. Want to know how and why your skin "tans"? I'm going to simplify the heck out of this, but the fundamentals are sound. Tanning is the result of increased melanin production, which darkens your skins. Melanin production is regulated in your dermis (the sod beneath your grass), and is triggered as a protective measure when the cells in the dermis are damaged. Think of it as a shield against further attack. The problem is two-fold: a) the shield/tan only goes up after at least one hit, because your dermis can't see the sun coming, and b) the shield is imperfect, as in it's better than nothing, but it only ameliorates future damage somewhat, it doesn't prevent it.

Depending on your skin type, you'll tan less or more in response to UVA exposure. Regardless of your skin type, however, the UVA rays will damage your dermis. Think about the dermis as scaffolding. When the scaffolding is in perfect shape, it fits below the skin smoothly; when it's damaged, it breaks down and provides less than perfect support, which appears as wrinkles and sagging on the skin layer above.

4. So, skin cancer. My primary interest in all this is the photo-aging aspect. I'm in a perennial war against wrinkles. But... skin cancer isn't pretty. In any sense of the word. Recent research shows that while UVB rays are the primary culprit, especially behind melanoma, UVA rays can not only cause basal and squamous cancers (the other two types), they evidently initiate, accelerate or enhance (well, from the cancer's point of view) UVB-caused cancer. This really shouldn't be much of a surprise, since suntans are evidence of cell damage and mutations, and cancer is a result of mutating cells (vastly over-simplified, I know, but do you really want a cancer monograph here?).

5. And, lastly, Vitamin D. Which isn't a vitamin at all, it's a hormone. And another post altogether. But it's true that UVB exposure is necessary for your body to make Vitamin D. Or you can take supplements and eat Vitamin D rich food (including salmon, mackerel, tuna, sardines, egg yolks). Go figure, Vitamin D deficiency has been (though not definitively) linked with an increased cancer risk, among other things. How's that for irony?

6. Oh, wait, and the whole SPF thing. If you've hung around me for any time, you probably already know that SPF only measures a sunscreen's efficacy against UVB rays. There is not yet a metric for UVA protection. It is clear, however, that until recently, sunscreens didn't contain ingredients that blocked both UVB and UVA rays. Now that they do, there is a whole 'nother host of issues to address. Aha! Yet another post.

By the way, it's the ozone layer that absorbs the really bad rays (UVC and some of the UVB). So as that goes...