bp's science: how sunscreen works (v.1)

When buying sunscreen, we all know to look for a specific SPF (Sun Protection Factor), and we understand that the higher it is the better protection we have. But do we know any more than that? As for me...not really. So let's learn together, eh?

The Sun Protection Factor is actually a multiplier value. Say for example your skin can handle 30 minutes of sun without getting sunburn. If you buy an SPF 15 product, then you can be out in the sun for 450 minutes (30 x 15) without getting sunburn. However, this value is determined assuming that people apply the sunscreen generously, but most people don't. In fact, most sunscreen users apply about 1/2 to 1/4 of the assumed amount. With that being the case, an SPF 15 product would truly only allow you stay out for 225 or 112 minutes, respectively.

There are three types of UV rays, UV-A, UV-B, UV-C. UV-A rays penetrate deep into your skin and cause premature aging and possible skin cancer. UV-B rays cause tanning and sunburn. UV-C rays are all absorbed by the earth's atmosphere (nothing to worry about there). The SPF factor specifies the protection against UV-B rays only. To ensure you're being protected from UV-A rays too, look for a sunscreen that specifies on the packaging that it has "broad spectrum" protection and you should be good to go.

The way sunscreen protects you is by reflecting and absorbing the sun's rays. Little inorganic particles (think zinc) in the sunscreen act like tiny bits of aluminum, and when a sun ray hits, the particles deflect it so the skin won't soak it in. Organic particles (think PABA) absorb the sun's rays so the skin doesn't have to. When the particles absorb the ray, the energy is released as heat. Keep in mind that sunscreen doesn't reflect or absorb 100% of all the of the sun's rays, so you're still getting some when you go outside. But that's a good thing, right? You've got to get your vitamin D somehow. But that's a discussion for another time.

With that said: Welcome spring! and sunscreen!

photo from a Labor Day badminton game, 2008


Chap said...

hey, thanks, I thought you would be able to be in the sun a lot less time than that! I probably err on the side of too much sunscreen!

Chap said...

is that Jess?

jo said...

very interesting information. i did not know this, and I was glad to get the lesson on "reflecting" and "absorbing". thanks for the info. i'm going to be better informed this summer.

Newport or bust!

ash said...

Yes, that is Jess playing badminton with a friend. Look at that form!

And yes, Newport or bust!

kel said...

thank you pb science. this is very helpful. now i am armed with SPF and knowledge!