Why you shouldn’t count on SPF for all of your sun protection
CBC
The SPF number printed on a bottle of sunscreen — meant to convey how much protection you’re getting — doesn't always match what's inside, a new CBC Marketplace investigation has found. That means Canadians who rely on sunscreen to protect themselves from the sun may be left with a false sense of security.
Marketplace sent a top-selling sunscreen labelled SPF 50 to five different accredited laboratories in Canada and the U.S. to test the product inside the bottle. We got back a roller coaster of results and an inside look at a testing system with almost no oversight.
The labs conducted the same test a manufacturer would to determine what SPF number to put on the label. All five told Marketplace the product was a different SPF: 34, 50, 60, 44 and 15.
CBC is not identifying the product tested since the process of determining an SPF was the focus of the investigation, not the product itself. Similar studies have shown that variability is surprisingly common in the sunscreen testing space.
“The results are really quite worrying, aren’t they?” said Brian Diffey, a professor emeritus of photobiology at Newcastle University in England who’s spent his career studying sunscreen and how people apply it.
They raise a question, he said: "Which one was right?”
Health Canada, which is responsible for regulating sunscreen in Canada, did not comment on Marketplace’s testing results.
There are two types of rays from the sun that can significantly damage the skin. UVA rays, or ultraviolet A, deeply penetrate the skin and can cause premature aging. UVB rays, meanwhile, penetrate the skin closer to the surface and can cause burns. Both types of rays can damage the DNA and cause skin cancers.
Any sunscreen labelled "broad spectrum" protects against both rays. But that familiar SPF number on the bottle refers only to protection from UVB rays.
SPF, which stands for sun protection factor, is calculated by measuring how long the skin can be exposed to UV radiation without burning using sunscreen, compared to without, in a controlled lab setting. An SPF of 30 means the skin will take roughly 30 times longer to burn, compared to without sunscreen, in the lab. Theoretically, the higher the SPF number, the higher the protection against UVB rays.
SPF 50, 30, and 15 respectively translate to roughly 98 per cent, 97 per cent and 93 per cent of UVB rays absorbed or reflected by the sunscreen.
The difference may seem small, but dermatologist Dr. Julia Carroll says it’s the percentage that’s getting in that we should pay attention to.
“It’s two per cent every minute, every second, it’s like a bucket dripping in,” she said. “I would rather have less UV radiation in my bucket at the end of the day, no matter what.”
The Health Canada- and U.S. Food and Drug Administration (FDA)-approved method of SPF testing is done on a panel of human volunteers. Manufacturers give a lab the estimated SPF value of their product, and the lab calculates the minimum amount of simulated sunlight required to slightly burn skin on a volunteer. SPF testing is only done on volunteers with light skin that fits within part of the Fitzpatrick skin type scale, so that sunburns are easier for lab technicians to see.
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