An SPF Testing Scandal Sheds Light on Sunscreen and its Flawed Ratings

Australia is synonymous with sunshine, so it’s no surprise that the country has the highest rates of skin cancer in the world.¹ Government guidelines state that sun protection is required whenever the ultraviolet radiation (UV) index is three or above. In Queensland—formerly known as the Sunshine State—the UV index is three or above all year; in summer, the UV index can exceed 11, which is considered extreme.

Extensive public health messaging initiated in the 1980s encourages Australians to avoid the damage of UV radiation by wearing protective clothing, hats, and, perhaps most importantly, sunscreen: The higher the sun protection factor (SPF) rating of a sunscreen, the better, and it needs to be reapplied regularly.

So, it came as a major shock to many Australians when an independent consumer report recently revealed that many sunscreens failed their SPF label claims. The “sunscreengate” scandal left consumers with a range of questions: How does sunscreen work? What do SPF labels actually mean? And if the SPF labels are wrong, should we even bother wearing sunscreen at all?

According to medicinal and supramolecular chemist Michelle Wong, whose science communication platform Lab Muffin Beauty Science aims to help people understand the science of skincare and beauty products, the problem is twofold. “Sunscreen is hard to make, but also, sunscreen is really hard to test,” Wong said.

How Does Sunscreen Actually Work?

The sun produces UV radiation with wavelengths ranging from 40 to 400nm. The Earth’s ozone layer absorbs the shortest UV rays, UVC (40–280 nm), so these higher-energy wavelengths don’t reach people. UVA (315–400 nm) has the longest wavelengths and can penetrate right down to the dermis of the skin; by breaking down collagen and elastin fibers there, it is a major contributor to the visible signs of aging, such as fine lines, wrinkles, and sagging. While UVB (280–315 nm) only reaches the epidermis, it causes direct damage to the DNA in skin cells, causing sunburn and blistering. Both UVA and UVB contribute to the development of skin cancer.²

“That's the reason that it is important to protect against the effect of sunlight on the skin,” said Henry Lim, a clinical dermatologist at Henry Ford Health and former president of the American Academy of Dermatology who has had a lifelong interest in photodermatology, sunscreen, and photoprotection. To protect skin from the harmful effects of sunlight, sunscreens need to be broad-spectrum, meaning that they are effective against both UVA and UVB radiation.

According to the first law of thermodynamics, matter can neither be created nor destroyed, so sunscreens need to convert the energy from UV light into something less harmful. There are two types of active compounds found in sunscreens that protect skin from UV radiation, widely referred to as “chemical” and “physical” sunscreens. However, Wong said these terms aren’t scientifically appropriate and have caused confusion among consumers; the more accurate way to describe them is as organic and inorganic sunscreens. “Chemical sunscreens are carbon-based [organic] compounds,” explained Wong. “They have lots of carbons linked together, and they have lots of aromatic rings and conjugation.”

According to Wong, this conjugation—the pattern of alternating single and double bonds in the structure of the molecule—allows the electrons to “run around,” spreading energy over a larger area. This phenomenon, known as delocalization, makes the molecules more stable. Which wavelengths are absorbed by a chemical sunscreen depends on the amount of conjugation in its structure. “In general, the larger the conjugated system, the longer the wavelength it absorbs,” she said.

In contrast, physical sunscreens—often referred to as mineral sunscreens—are made up of inorganic particles, primarily zinc oxide and titanium dioxide. “The active ingredients absorb UV and turn it into heat, and that's the case for both chemical and physical sunscreens,” Wong said. Physical sunscreens also reflect or scatter UV radiation to a degree.

Challenges in Formulating Sunscreen Products

The idea of a perfect sunscreen is an elusive concept. Often, to achieve very broad-spectrum protection, sunscreens contain both chemical and physical filters. Physical filters, such as those containing zinc oxide, can be a major challenge when it comes to formulating a sunscreen product. Unlike chemical filters, which can easily dissolve, zinc particles do not, Wong explained. “They're much denser than the other ingredients in sunscreens, which are usually oils and a bit of water, so they're going to sink. They're going to want to separate a lot more than chemical sunscreen [ingredients].” These active ingredients also need to be photostable, meaning that they don’t break down rapidly when exposed to sunlight.

Aside from the active ingredients, sunscreens contain emulsifiers, preservatives, and other minor ingredients like fragrances; these allow the active ingredients to spread over and bind to the skin, give it a long shelf life, and allow for water resistance, among other things. “The rest of the sunscreen in itself has to spread these molecules out so that they can cover all of your skin and keep them spread out for a long enough period of time,” said Wong.

How well a sunscreen actually works is also based on factors beyond the control of the companies that develop these products. One of those factors is the texture of human skin, which is not a smooth surface but a bumpy, moving landscape. “When [sunscreen] dries down, water is evaporating, ingredients are absorbing and mixing with the top layers of skin, and then that film is forming,” said Wong. User error is also a key contributor to reduced effectiveness, with many consumers not using enough of the product to be adequately protected.

Sunscreengate Revelations Lead to Mass Recalls of Australian Sunscreens

The testing that initiated the sunscreengate scandal in Australia was led by consumer watchdog CHOICE. After testing 20 sunscreen products, CHOICE reported publicly that 16 products failed their SPF label claims. One of the products tested as low as one tenth of its reported SPF. The Australian Cancer Council, the country’s leading cancer charity, produced some of the sunscreens, and some were listed on their website as Australia’s most trusted sun protection.

John Staton, a molecular biologist and SPF testing expert with more than 60 years of experience in the pharmaceutical and personal care industry, works as a consultant for developers of sunscreen products around the world. Although he is no longer involved in its operations, Staton founded the lab that CHOICE selected for SPF testing. The lab was also approved by the Australian government’s regulatory authority, the Therapeutic Goods Administration (TGA). “I have every confidence in the results,” Staton remarked. “The lab that tested [the sunscreens] is very experienced.”

The fallout was rapid and extreme; many brands insisted their original testing was compliant and accurate and then scrambled to perform more independent tests that verified those original claims. Shortly afterward, several companies began recalling their products or halting production. At least 21 different products using the same base formula as the worst-performing zinc-oxide-based product were also recalled.³ Wong wasn’t surprised by this result. “In almost all of these third-party sunscreen tests, [zinc oxide-based formulas] almost always do worse because they are just much harder to formulate.”

What is apparent to experts, but may be less obvious to consumers, is that the onus does not fall squarely on the shoulders of companies that produce sunscreen products, but rather it falls somewhere between the producer and the many different laboratories that offer SPF testing. Because sunscreens are considered therapeutic goods, Staton said, companies need to conduct due diligence when choosing a testing lab, since not all of them are created equal. “The temptation is always there [for sunscreen developers]: ‘Who gives me the highest result, and how quickly can I get it?’” Staton added.

In the aftermath of the scandal, one of the third-party SPF testing labs commonly used by sunscreen producers to test their products, Princeton Consumer Research, was found to have produced inaccurate results and is now plagued with broader concerns over its testing practices. According to Lim, however, the variability in testing may not just be due to dodgy lab practices but also could result because testing procedures are complicated. “The limitations that led to the sunscreengate scandal in Australia are that it is very subjective [SPF] testing,” said Lim. “The testing is done completely by trained individuals, but it is still subjective.”

SPF Testing Methods: Why Can’t We Agree?

SPF testing procedures fall broadly into the categories of in vivo and in vitro. “[About 15 years ago,] Australia decided that we should go along the pathway of what's called harmonization, which means we're all supposed to be following the same procedures, and everyone agrees on everything,” Staton explained of SPF testing procedures. “That's far from the truth of how the process works because people, right from the beginning, had ideas about in vivo and in vitro testing.”

The gold standard and most widely used method is in vivo testing on human skin, outlined by the ISO 24444 protocol. Typically, scientists measure and mark out patches on the backs of fair-skinned volunteers, applying a specific amount of product to one patch and leaving another unprotected. “It's two milligrams per centimeter square that you apply on the skin, and that is definitely higher than the average individual would use in a real-life situation,” Lim said.

The testers use a solar simulator to imitate the effects of sunlight in incremental doses. “They shine the UV light onto bare skin versus the sunscreen-covered skin, and they look at how much UV it takes to make both go slightly pink, and they [assess] the difference between those,” Wong explained. “[You end up with] a ratio. If it's SPF 50, it means it took 50 times more [UV light to go pink] with the sunscreen on.”

One of the key issues with in vivo methods, Lim said, is their inherent lack of objectivity: “A trained human being would still have to evaluate the redness induced by [the solar simulator], so there is quite a bit of subjectivity in that.” The variability in skin types among the subjects also complicates this method.

In vitro methods of SPF testing have been developed in the last couple of decades. These assays, such as the ISO 23675 protocol, were designed to eliminate the need for testing in human subjects and to improve the consistency and accuracy of testing procedures. They typically involve applying the product to plastic plates, shining the solar simulator on it, and using spectrophotometry to measure how much UV light gets through.

However, because human skin is a moving, bumpy surface, it is very different from a plastic plate. “There's no doubt the in vitro method is going to be very objective, because whatever numbers you get, whatever transmission curve you get, is a transmission curve,” said Lim. “But it does not take into account the biological response of human skin.”

Despite this key shortcoming, in vitro methods are being optimized and are gaining traction. “There's two new [in vitro] methods, and they seem to be valid,” Wong said. “They seem to match up with in vivo SPF testing most of the time.”

Changing Labels and Managing Consumer Expectations

In the wake of sunscreengate, the TGA responded to consumer concerns by suggesting that they might remove SPF labels from sunscreens entirely. Instead, sunscreens would be labelled as one of four broad categories: low, medium, high, or very high protection. These categories would be based on ranges of SPF numbers, but no numbers would actually be included on the label.

Wong said that she welcomes the TGA’s proposal. “That part has been a long time coming,” she commented. “Honestly, looking back on it, having specific SPF numbers was a mistake because it gives so much false precision.” Lim is also in favor of the change. “In principle, it is probably easier for the consumer to understand what type of sunscreen they are buying,” he said.

Regarding whether Australians should still bother wearing sunscreen, Wong was quick to point out the vast amount of clinical data that supports the efficacy of even low-protection sunscreen products. “[In one study,] an SPF 16 sunscreen from the 1990s gave all these reductions [in the incidence of skin cancer and melanoma, specifically]. I think it almost halved [it],” she said. “So, there are a whole bunch of massive benefits from SPF 16.”

Lim, who works with the FDA on the regulation of sunscreen products in the US, said that the TGA has approved a greater range of active compounds for sunscreen products than are available in the US. “The major issue right now for the FDA is that we don't have many of the UV filters that are available in many parts of the world,” he said. In June, the FDA approved a new UV filter, bemotrizinol, for the first time in 20 years.

The final consideration for people when protecting themselves from the sun, Lim said, is that they must layer their protection. “I want to emphasize that photo protection is not only sunscreen alone,” he said. “It is more about staying in the shade when outdoors, wearing appropriate protective clothing, a hat, and then a sunscreen on the exposed areas of the body, and of course, sunglasses.”