You may be surprised at the rigorous trials sunscreens go through to prove they work as promised — especially to earn The Skin Cancer Foundation’s Seal of Recommendation.
Before sunscreens appear on store shelves in the U.S., manufacturers must perform testing according to FDA guidelines to prove the claims on the label, from sun protection factor (SPF) to water resistance. This helps assure consumers that a product will protect them and their families in the way the label promises.
Testing is done in a laboratory, and nearly all of the tests use paid “real people” as subjects. We asked expert Steven Q. Wang, MD, director of Dermatologic Surgery and Dermatology at Memorial Sloan Kettering Cancer Center in Basking Ridge, New Jersey, to describe how the tests work.
Sun Protection Factor
WHAT IT IS: SPF represents a sunscreen’s degree of protection mainly against ultraviolet B (UVB), the sun’s shorter wavelength rays, which cause sunburn and can lead to skin cancer. SPF doesn’t represent an amount of sun protection but rather a length of time. It gauges how long the sun would take to redden your skin when using a particular sunscreen compared with the amount of time without sunscreen. For example, if you use an SPF 15 product under ideal circumstances (meaning you use enough, apply it evenly and don’t sweat it off), it would take you 15 times longer to burn than if you weren’t using sunscreen.
HOW IT'S TESTED: In the lab, experts first analyze volunteers’ tendency to burn by shining a UV lamp, simulating solar rays, on the skin of their backs. This determines the amount of time in the sun that it takes to make their unprotected skin red. Then a lab technician carefully applies a specific amount of several sunscreens to measured-out squares on the volunteers’ backs, rubs it in, waits 15 minutes for the sunscreen to absorb and then directs the solar simulator on the skin again. If, say, an SPF 30 sunscreen is being tested, and the patch of protected skin goes 30 times longer than the unprotected skin before reddening, it proves that the product is at least an SPF 30. This test is done on at least 10 paid volunteers, and the average result confirms the SPF rating.
WHAT IT IS: To claim broad-spectrum protection, a sunscreen must protect against the sun’s long-wave ultraviolet (UVA) rays as well as UVB. Like UVB rays, these can cause cancer, and they are the major cause of premature skin aging.
HOW IT'S TESTED: Testing for UVA protection doesn’t require human volunteers; it is strictly a lab test. Technicians carefully apply the sunscreen to a special material in a lab dish. They then shine light on it, simulating the rays of the UV spectrum, and measure UV absorption. UV wavelengths are measured in nanometers (nm), or billionths of a meter. The waves in the UVB portion of the light spectrum are relatively short, from 290 to 320 nm. UVA waves get progressively longer, from 320 to 400 nm. A mathematical equation is used to convert the test results into a graph called an absorption curve. “To pass the broad-spectrum test,” Dr. Wang explains, “90 percent of the area under the absorption curve must be above 370 nm.” The test is repeated to make sure the product is photostable, meaning the ingredients don’t break down after exposure to UV rays but continue to protect the skin.
WHAT IT IS: While sunscreens can’t claim to be waterproof, they can be labeled water-resistant for either 40 or 80 minutes.
HOW IT'S TESTED: In the laboratory, technicians apply the sunscreens to the volunteers’ backs. These subjects then sit in a laboratory version of a hot tub. “You want to create a bit of turbulence in the water to simulate reality,” says Dr. Wang. “The volunteers sit in this tub together for 40 or 80 minutes, depending on what the sunscreen label claims.” When the volunteers come out of the water, the SPF test is repeated to make sure the product didn’t wash off but still protects the skin from UV rays. Ten volunteer results are required to pass this test.
The Seal of Recommendation Goes Further
The Skin Cancer Foundation’s Seal of Recommendation has two categories for sunscreens: SPF 15 or higher protection for the “Daily Use” Seal, meant for limited sun exposure, and SPF 30 or higher for the “Active” Seal, meant for more extended time outside. To earn the Seal, manufacturers must submit an application including a wide range of testing data. Then the Foundation’s Photobiology Committee of renowned UV experts carefully reviews the application and data to ensure they meet all the Foundation’s standards. Dr. Wang, chair of the committee, says that to earn either Seal, manufacturers must pass two additional tests that go beyond FDA requirements:
WHAT THEY ARE: The first of these tests is for “contact irritancy” — an allergic reaction or rash that occurs before sun exposure when you apply the sunscreen. The second is for “phototoxicity,” an allergic reaction or rash from sunscreen that occurs specifically after the skin is exposed to UV light.
HOW THEY'RE TESTED: To test for contact irritancy, a technician applies sunscreens on volunteers in small patches on the skin. Volunteers return to the lab in 24 hours to see if any products caused a skin reaction or rash. To test for phototoxic reactions, the lab applies sunscreens to specific areas on the volunteers, then exposes those areas to the UV light source to see if there are skin reactions. For a product to receive the Seal, 20 volunteers must have passed these tests with no such reactions. By the time a sunscreen has passed all of these tests and earned the Seal, consumers can be confident about the product’s safety and effectiveness.
Chemical Versus Physical
“People always try to define whether a sunscreen is chemical or physical, but it’s really a misnomer,” says Dr. Wang. All active sunscreen ingredients are chemically derived. There are two categories of ingredients, he explains. The ones many people call “chemical” are actually “UV organic filters.” These include ingredients such as avobenzone and benzophenone, and they work by absorbing UV rays. There are also two so-called “physical” ingredients: titanium dioxide and zinc oxide. Some people may think of them as more “natural,” or even “organic,” but they’re actually inorganic mineral compounds, says Dr. Wang. They work by staying on top of the skin and deflecting and absorbing UV rays. While physical sunscreens may be less likely to cause skin irritation than “chemical” sunscreens, both types have been tested as safe and effective. In fact, many sun protection products available today combine both types of ingredients.
Illustrations by Lily Padula
Published on May 19, 2016