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Your guide to summer sunscreen use

- Samantha Rideout

YOU ALREADY KNOW the basics: apply sunscreen liberally and repeat often. But there’s more to be done if you want to get the best protection from harmful rays.

Know your numbers

An SPF of 15 filters out about 93 per cent of cancer-causing UVB rays, while an SPF of 30 protects against 97 per cent of them. SPF 50 stops 98 per cent, and SPF 100 stops 99 per cent. So the higher the SPF, the more marginal the difference—and no sunscreen is able to protect you from all UVB rays.

Mind the A rays

Both UVA and UVB rays contribute to cancer and premature skin aging, but UVAs are sneakier—they don’t cause burns. To make sure your sunscreen is keeping both at bay, look for the phrases “broad spectrum,” “multi-spectrum” or “UVA/UVB protection” on the label.

Make sure you get enough