What SPFs actually mean

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You may be as well off with SPF 15 as with SPF 60.

I heard an interesting comment from GP Rosemary Leonard on the telly the other day, saying that you don’t get much more protection from SPF 60 than you do from SPF 15.

Could this be true, I wondered.

In fact, she’s right. 

SPF is measured on the multiples of minutes that you can spend in the sun without burning. IE: wearing SPF 15 means you can spend 15 times longer in the sun without burning than if you don’t wear any protection at all. So if, on a normal day you’d burn in 10 minutes, SPF will protect you for about 2.5 hours.

In theory, then, you should be able to stay out for 60 times longer if you wear SPF 60. But the problem is, you can’t, because the effectiveness of sunscreen drops over time.

SPF 60 does protect you a little better than SPF 15. But that word is a little. Look at this chart of percentage of protection from damaging UVB rays:

SPF 15 screens 92% of UVB

SPF 30 screens 97% of UVB

SPF 40 screens 97.5% of UVB

SPF 50 screens 98% of UVB

SPF 70 screens 98.5% of UVB

SPF 100 screens 99% of UVB 

As you can see – SPF 15 is already protecting you from the vast majority of UV rays. And where this really counts is in cost – SPFs 30 and 60 cost vastly more than SPF 15, so if cost is an issue in these tight times, use SPF 15, apply it more thickly and apply it more often. Every two hours is about right.  

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