New sunscreen labels in effect this year require a pass-fail test for UVA and UVB protection.

WSJ: European Sunscreen Roadblock on U.S. Beaches

Both UVA and UVB rays contribute to skin cancer, but the damage caused by UVA rays is harder to measure.

WSJ: European Sunscreen Roadblock on U.S. Beaches

Meanwhile, avobenzone can break down in sunlight, experts say, and reduces the potency of octinoxate, a UVB filter common in the U.S., when combined with it.

WSJ: European Sunscreen Roadblock on U.S. Beaches

On top of that, sunscreens can be labeled "broad spectrum" only if they protect equally against UVB (the main culprit of skin cancer) and UVA rays, which cause aging.

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In winter, experts say, people in the northern half of the U.S. don't receive enough UVB rays from the sun to make vitamin D, regardless of whether they use sunscreen.

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