The original meaning of "SPF" – Sun Protection Factor – just doesn't serve us any more.
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The original meaning of "SPF" – Sun Protection Factor – just doesn't serve us any more.
We all have to FORGET what "SPF" actually means; here's why.

Any longtime beauty editor or beauty writer will tell you that context is everything when it comes to understanding formulas or ingredients or skincare and makeup trends. Most of us know contouring, strobing and baking as decades-old, standard makeup-artist techniques. We got grabby hands for serums in the late 2000s to get higher concentrations of active ingredients into the top layer of our skin. And we know what the term SPF is supposed to mean: that you can spend X more minutes in the sun without suffering a painful burn. 

But we all need to forget that last one.

SPF – Sun Protection Factor – was a concept created by a major sunscreen company as a marketing aid to explain and differentiate strengths of anti-sunburn cream.

The idea was that something like an SPF 10 would give you 10 times longer in the sun without a sunburn. If your bare skin got red in 10 minutes, the premise was that SPF 10 would let you stay out for 100 minutes without turning into a lobster. (UPDATE 19 AUG 2017: Here's an excellent post from Michelle at LabMuffin.com on the specifics of how sunscreen is tested, and why SPF doesn't work as a measure of extra time in the sun.)

That concept and measure of protection is quite simply OBSOLETE, invalid, and here's why: 

  1. The term SPF was created in a time when there was an SPF 10, even SPF 4. "That's from the 1950s," says dermatologist Julia Carroll, co-director of Compass Dermatology in Toronto. "And the SPF number is theoretically about the burn, the UVB rays." 

  2. In the decades since the invention of the SPF concept, we've learned about the more insidious danger of UVA rays. "Now it's about the long-term effects," says Dr. Carroll. "Sunscreen now is also supposed to protect you from UVA, which causes deeper, long-term damage that can affect your DNA. It's about preventing cumulative sun damage."

  3. In 2012, Health Canada banned any suggestion on sunscreen packaging that the product within "allows you to stay longer in the sun." (In the same document, they ruled against using the word "sunblock," as well as "waterproof.")

Crucial now is broad spectrum protection that promises defence against UVA and UVB rays. We've seen what UVA can do in years of repeated exposure. Remember poor truck driver Bill McElligott?

Career truck driver Bill McElligott is the face of UVA damage.

Career truck driver Bill McElligott is the face of UVA damage (your right, his left)

And rather than what SPF means, we need to think about SPF numbers in terms of how little UVA/UVB they let into our skin over time. When applied as directed – aka generously – SPF 15 keeps about 93% of the sun's UVA/UVB rays out; SPF 30 is effective against almost 97%. 

Although SPF 50, 60 and up offer just a fraction more protection, the simple fact is that the higher the number of the sunscreen we use, the lower the percentage of UVA/UVB leaking through during our entire lifetime. SPF 50 is the new SPF 30, you know?

That's my sunscreen philosophy anyway. What's yours?

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