Today is the last day of spring, and summer starts tomorrow.  So have you stocked up on sunscreen yet?  If not, here's some free advice on what to buy.

We'd always heard that super-high SPFs were kind of pointless.  That there's not much difference between SPF 50 and SPF 100.  But according to a recent study, that's NOT actually the case.

Researchers in Colorado tested different levels of SPF on skiers.  Each person had to put SPF 50 on one side of their face, and SPF 100 on the other side.

And the side with SPF 50 was 11 times more likely to end up with sun damage.

The study found there are two main reasons it happened, First, that extra SPF does protect your skin a little better.  SPF 50 blocks about 98% of UV-B rays, compared to 99% with SPF 100.

But the main reason is most of us don't apply as much sunscreen as we're supposed to and don't RE-apply it enough.  And higher SPFs offer a little more leeway in that regard.  So you're more likely to be protected, even if you don't put enough on.

In general, SPF 30 is good enough.  But only if you put it on thick.  And only if you re-apply it every two hours.