1. How can you tell if a sunscreen effectively protects against ultraviolet B radiation—the type that can cause sunburn and other skin damage and contributes to skin cancer?

That’s right. Protection against UVB radiation is indicated by a sunscreen’s sun-protection factor number. Look for one with an SPF of at least 30; those with higher numbers can also be good choices, though 30 is plenty for most people. There’s still no rating system for protection against the more deeply penetrating ultraviolet A radiation, but the Food and Drug Administration plans to adopt one this year. Still, it may be a while before you see it on product labels. “Broad spectrum” implies that a product also blocks UVA rays in addition to UVB rays, but it does not tell you how effective the product is at doing so.

No. The sun-protection factor number tells you how well a product blocks UVB rays. Look for one with an SPF of at least 30; products with higher numbers can also be good choices, though 30 is plenty for most people. There’s still no rating system for protection from the more deeply penetrating ultraviolet A radiation, but the Food and Drug Administration plans to adopt one this year. Still, it may be a while before you see it on product labels. “Broad spectrum” implies that a product also blocks UVA rays in addition to UVB rays, but it does not tell you how effective the product is at doing so.

2. Which of these sunscreen ingredients guard against ultraviolet A radiation—the more deeply penetrating type that can contribute to skin cancer and cause sunburn, wrinkles, and age spots?

You’re partially right. The answer is all of the above. Avobenzone’s ability to absorb ultraviolet light over a wide range of wavelengths has led to its use in many sunscreens labeled as broad spectrum, though its performance in any sunscreen depends on the overall formulation.

You’re partially right. The answer is all of the above. Zinc oxide is a mineral-based ingredient known for its ability to protect against UVA rays, though its performance in any sunscreen depends on the overall formulation.

You’re partially right. The answer is all of the above. Titanium dioxide is a mineral-based ingredient used in sunscreens, which can provide some protection against UVA rays, though its performance in any sunscreen depends on the overall formulation.

Yes. All three ingredients help protect your skin from UVA rays. The performance of each of these ingredients in any sunscreen depends on the overall formulation.

3. Research has raised some concerns about the potential health risks of nanoparticles used in some sunscreens. Are sunscreen makers required to identify those very small engineered ingredients on their product labels?

Wrong. Manufacturers don’t have to tell you anything about nanoengineered ingredients. So what’s a concerned consumer to do? Check out the list of ingredients on the sunscreen label. Zinc oxide and titanium dioxide are common mineral-based active ingredients in sunscreens that are often engineered to be nano-size in part to make them look clearer on skin. If you want to avoid these nano-scale ingredients, choose sunscreens that use other active ingredients instead. You won’t have to settle for less sun protection. Our 2007 tests of sunscreens found no correlation between effectiveness and the presence of those ingredients.

You’re right. Manufacturers don’t have to indicate on the label if an ingredient is an engineered nanomaterial. So what’s a concerned consumer to do? Check out the list of ingredients on the sunscreen label. Zinc oxide and titanium dioxide are common mineral-based active ingredients in sunscreens that are often engineered to be nano-size in part to make them look clearer on skin. If you want to avoid these nano-scale ingredients, choose sunscreens that use other active ingredients instead. You won’t have to settle for less sun protection. Our 2007 tests of sunscreens found no correlation between effectiveness and the presence of those ingredients.

4. Is it important to choose a product that claims it is PABA (para-aminobenzoic acid)-free?

Wrong. A "PABA-free" label is mostly a marketing ploy that may do more to confuse consumers than educate them. Virtually no sunscreens sold in the U.S. still contain PABA, an older sunblocking ingredient that causes allergic reactions and possibly other problems. If you are concerned check the ingredient label.

You’re right. A “PABA-free” label is mostly a marketing ploy that may do more to confuse consumers than educate them. Virtually no sunscreens sold in the U.S. still contain PABA, an older sunblocking ingredient that causes allergic reactions and possibly other problems. If you are concerned check the ingredient label.

5. Is there such a thing as waterproof sunscreen?

Not really. No sunscreen is really waterproof, as far as the Food and Drug Administration is concerned, but some manufacturers use the term to mean very water resistant. Sunscreens labeled as either waterproof or very water resistant should maintain their effectiveness even if you’ve been in the water for up to 80 minutes or if you sweat heavily. With those labeled water resistant, you can stay in the water for up to 40 minutes.

That’s right. No sunscreen is really waterproof, as far as the Food and Drug Administration is concerned, but some manufacturers use that label to mean very water resistant. Sunscreens labeled as either waterproof or very water resistant should maintain their effectiveness even if you’ve been in the water for up to 80 minutes or if you sweat heavily. With those labeled water resistant, you can stay in the water for up to 40 minutes.

6. Nearly three-quarters of sunscreen-users in our survey said they want a sunscreen with vitamin D. Is that a good idea?

You’re probably wrong. While research suggests that many Americans are low in vitamin D, possibly in part because of the increased use of sunscreen, it’s unlikely that rubbing the nutrient onto your skin will have a meaningful effect on your blood level of the vitamin. And in any case, none of the products we’ve seen said they contained vitamin D.

You’re probably right. While research suggests that many Americans are low in vitamin D, possibly in part because of the increased use of sunscreen, it’s unlikely that rubbing the nutrient on your skin will have a meaningful effect on your blood level of the vitamin. And in any case, none of the products we’ve seen said they contained vitamin D.