Introduction

Which sunscreen ingredients protect best?

If the sheer number of sunscreens available isn't confusing enough for consumers, then the conflicting information about sunblock certainly is. Sunscreens are available in a variety of preparations (sprays, lotions, creams) and potencies (SPFs from 15 to 100), but the SPF number doesn't tell the whole story.

UVA vs. UVB rays

There are two types of skin-damaging ultraviolet (UV) rays: UVB rays, which cause common surface sunburns, and UVA rays, which trigger deeper damage to connective tissue (including skin cancer and the wrinkles and sunspots associated with premature aging). In addition, there are two kinds of skin-damaging UVA rays – short and long.

UVA rays are longer (320 to 400 nanometers) and penetrate the skin at deeper levels than UVB rays, causing long-term damage associated with signs of aging and skin cancer. According to the Skin Cancer Foundation, these rays are "present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass."

UVB rays, on the other hand, are shorter (290 to 320 nanometers) and are responsible for visible damage to the skin in the form of sunburns. Unlike UVA rays, the intensity of UVB rays varies by season, location and time of day. In the United States, UVB rays are most intense between the hours of 10 a.m. and 4 p.m., from April to October.

Ingredients make all the difference

Experts say a good SPF sunscreen should protect users from both UVA and UVB rays. The best formulas should contain broad-spectrum chemical or physical sunscreens or a combination of the two. A product's ingredients are directly connected to its level of protection.

Physical sunscreens are made with minerals (titanium dioxide and zinc oxide) that form a natural, protective layer on the skin that blocks the sun's harmful rays. Chemical sunscreens (avobenzone, Mexoryl SX and Tinosorb) absorb UV rays. It's important to note that some chemical SPF sunscreens, including the commonly used oxybenzone, can protect only against a portion of UVA waves (those in the lower end of the UVA spectrum).

Many sunscreens contain oxybenzone, but they don't contain anything to protect against long-wave UVA. By including oxybenzone, companies are allowed to say their product protects against UVA, but unless it also contains avobenzone, zinc oxide, titanium dioxide or Mexoryl SX, experts say users are not optimally protected against long-wave UVA rays.

Mexoryl SX is a highly publicized ingredient that has been used in Canada and Europe since 1993, and it was approved by the Food and Drug Administration (FDA) for use in the U.S. in July 2006. However, sunscreen products containing Mexoryl SX (a trademark of L'Oreal) have been slow to enter the U.S. market. Initially only a handful of products with Mexoryl, all made by L'Oreal-owned companies, were available in the U.S., but the number is growing.

Although Mexoryl SX received a lot of attention when it was first introduced in the U.S., excitement has since waned and Paula Begoun, skin care expert and author of "Don't Go to the Cosmetics Counter Without Me," remains skeptical. She agrees that products using Mexoryl SX offer reliable UVA protection, but she says the formulas available are expensive and don't contain many other beneficial ingredients, such as antioxidants.

Begoun also says Mexoryl SX doesn't offer the best possible protection."Although Mexoryl SX is a good UVA sunscreen," she says, "it does not provide the highest level of UVA protection as claimed on the label." Natural sun-blocking formulas containing titanium dioxide and zinc oxide provide greater levels of protection, she adds. The bottom line: Mexoryl SX is an effective broad-spectrum sunscreen, but it's expensive and other options are also viable.

Health concerns about sunscreen use

Some of the newest sunscreen products use nanotechnology to make formulas that are more aesthetically pleasing. Nano-sized titanium dioxide and zinc oxide particles are much smaller than the typical micronized particles contained in most SPF sunscreens. The smaller particle size allows them to go on more smoothly without leaving a noticeable white cast on the skin. Some consumer advocates warn that nano-sized particles can penetrate the skin and are potentially hazardous.

However, the Cancer Council of Australia says these particles cannot penetrate the skin deep enough to be absorbed into the bloodstream, and there is no evidence of any risk associated with their use. Begoun agrees, pointing out that there is no scientific proof that these sunscreens are absorbed into the skin. "Actually, you wouldn't want that to happen regardless of any potential risk because sunscreen actives need to remain in the surface layers of skin in order to protect it from UV damage," she says.

Other controversial issues: In a 2012 report, The Environmental Working Group (EWG) found that only 39 of 500 sunscreens in their study provided acceptable protection. According to the EWG, a consumer watchdog organization, many SPF sunscreens don't provide adequate UVA protection and contain chemical ingredients that may be harmful to the skin. However, several experts, including the American Academy of Dermatology, have since criticized the study.

Regardless, most experts say sun exposure is more harmful than the other possible side effects of some sunscreens and suggest that until further studies are available, consumers should continue to use broad-spectrum sunscreens of all types. However, because of increasing interest in the topic, we have included a section on natural sunscreens (products that use fewer chemicals) for concerned consumers.

Additionally, some question whether sunscreens trigger vitamin deficiencies. Some experts have suggested that daily sunscreen usage can increase a person's risk of developing a vitamin D deficiency, because the sun is the most readily available source of this nutrient. Dermatologists, however, say sunscreen is necessary to reduce the risk of skin cancer. Ultimately, medical experts say this: Skin cancer is a proven threat -- and the only real way to reduce risk is to limit sun exposure by staying indoors, wearing protective clothing and using broad-spectrum sunscreen.

If you're concerned about a deficiency, speak to your doctor. Sunshine aside, Vitamin D is also available in supplements and certain foods. See our report on multivitamins for noteworthy options. Our blog post on the topic also provides further insight into this debate.