It's summer here in the northern hemisphere
which means we're seeing a whole lot more sunscreen
every bottle has a big SPF number on it
and a lot of us probably assume we know what those numbers mean
higher numbers equal more protection, right?
Well yes, but also no It's a little more complicated
The thing is, you probably don't need more than SPF 30 or so
And there are bigger things to worry about
like whether you're wearing enough sunscreen to really protect your skin
SPF stands for sun protection factor
It's a measure of how much less of the dangerous ultraviolet radiation from the sun
hits your skin with sunscreen on than without it
Two types of ultraviolet light can reach Earth's surface called UVA and UVB
They have different energy levels and affect our bodies in slightly different ways
UVB is the main cause of sunburns
and it's directly linked to the development of skin cancers
And UVA leads to tans which happens when your body
makes compounds to stop UVA from damaging too many skin cells
SPF in the United states is only calculated based on
how much UVB gets blocked since we really only knew about UVB's risks
when making the standards
So if you wear SPF 30 the general idea is that your skin
absorbs about 30 times less UVB than it would without sunscreen
Because chemicals absorb or reflect the radiation to block it from getting into your cells
This roughly translates to SPF 30 blocking 96.7% of UVB
If you wear SPF 40 your skin absorbs 40 times less because it blocks around 97.5% of UVB
And even when you get up to SPF 100 that only blocks around to 99% of UVB
That's not a super huge difference
So most people get no added benefit from wearing anything above SPF 50
And SPF 30 is usually plenty
But that's only true with the right amount of sunscreen
And people, well we're not very good at wearing it
For one thing if you remember to wear sunscreen in the first place
most of us only wear about a third of what we should
Not to mention we're pretty sweaty
Sweat and water makes some sunscreens come off more easily
and even the best waterproof stuff still breaks down or rubs off after a couple of hours
So experts recommend reapplying sunscreen every two hours
regardless of its SPF
But even with the right amount on some of us still don't get all of the protection we need
Since making those initial SPF standards we've learned that both UVA and UVB radiation
can damage DNA and kill skin cells and both are strongly linked to skin aging and cancer
So to be safe, you should always get a sunscreen with a broad-spectrum SPF
which measures both UVA and UVB Blockage
Basically SPF is important
But there's a lot more that goes into wearing sunscreen so you can make sure it's actually doing its job
We're uploading summer themed videos all week
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And if you want to impress your friends with science while you're swimming
check out these awesome new scishow beach towels available at dftba.com/scishow