A recent lawsuit has grabbed headlines and raised consumer concerns with its claim that Skittles, the popular many-colored candies, contain “a known toxin”: the chemical titanium dioxide. The suit, filed by a consumer in July against Skittles manufacturer Mars, notes that the European Union is banning titanium dioxide as a food additive.
But in the U.S., Canada and many other countries, titanium dioxide is still deemed safe for consumption, within regulated amounts. So what does the science actually say about the chemical, which is also used in cosmetics and sunscreens? Scientific American reached out to several toxicologists who have studied whether titanium dioxide can cause harm to get some answers. (We also asked Mars to comment but did not receive a response by the time of publication.) It turns out there is no conclusive research showing the chemical, as it is used in food products, poses danger to people. Some hints from animal studies have prompted European countries to act out of an abundance of caution. Yet “saying we’re not certain that it’s safe is very different from saying it’s unsafe,” says Agnes Oomen, a senior scientist at the Netherlands’ National Institute for Public Health and the Environment, who has studied the chemical.
What products include titanium dioxide, and why do they use it?
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Titanium dioxide is a naturally occurring odorless white powder used as a pigment in a large number of candies, including Skittles, as well as in a range of other products, such as cosmetics and even house paint. It’s excellent at scattering visible light, which gives whatever it’s added to a brighter, richer color. Titanium dioxide is also popular in sunscreens because of its effectiveness against skin-harming ultraviolet rays.
How is titanium dioxide regulated in the U.S.?
In the country, the Food and Drug Administration considers the chemical safe in foods, drugs and cosmetics. As a color additive in foods, the FDA requires that titanium dioxide meet certain specifications. One is that its quantity cannot exceed 1 percent by weight of the food to which it’s added.
Why is the chemical being banned in the E.U.?
In Europe, titanium dioxide as a food additive is being phased out alongside what’s predicted to be thousands of other chemicals in a variety of products. The effort is sometimes referred to as the “great detox.”
The impending ban on titanium dioxide is the result of the European Food Safety Authority (EFSA)—an agency that issues scientific advice on food risks—evaluating the safety of the chemical as a food additive in a 2021 report. EFSA noted that it could not definitively say that titanium dioxide was toxic. But it also could not rule out the possibility that the substance could be genotoxic—a term that indicates something can change genetic material, including DNA—or establish a safe level for daily intake. Because of such uncertainties, EFSA concluded that titanium dioxide could no longer be considered safe when used as a food additive.
Oomen, who was one of the authors of the EFSA report on titanium dioxide’s potential toxicity, says the decision “is on the cautious side.” For the past 15 years, she has been working on evaluating the risk of nanoparticles to human health. These are particles sized from one to 100 nanometers, and some food-grade titanium dioxide particles fall into that range. Breathing in nanoparticles has long been established as hazardous to human health, but when it comes to ingesting them, there’s less of a scientific consensus. Still, Oomen, who is also a professor at the University of Amsterdam, wonders “if it’s just being used as a colorant, is it really necessary to have in your food?”
“I think the main issue around titanium dioxide right now is not the science; it’s that the European Union very much wants to get rid of nanomaterials in food,” says Norb Kaminski, director of the Institute for Integrative Toxicology at Michigan State University. (Kaminski has, in the past, consulted for the Titanium Dioxide Manufacturers Association.)
Have there been problems with toxicity studies?
According to Kaminski, the majority of studies assessing the toxicity of titanium dioxide have been done in animal models, primarily rats. In a 2017 study prominently mentioned in EFSA’s safety assessment—the same study that has been credited with prompting France to ban the chemical in food in 2020—researchers added titanium dioxide to rats’ drinking water. After 100 days, the researchers found these rats were more likely to have developed aberrant crypt foci—clusters of abnormal glands in the lining of the colon and rectum—than were rats given regular drinking water. The abnormal glands can foreshadow colon cancer.
But this study has a critical experimental flaw, according to some researchers: titanium dioxide does not dissolve in water, so it likely sank down and gathered in large amounts near the opening of the bottle from which the rats were drinking. “So we have absolutely no idea what amount of titanium dioxide these animals were exposed to,” Kaminski says. “Remember that enough of anything—even things like water and oxygen—can be harmful.”
Eric Houdeau, one of the 2017 study’s authors and a research director at France’s National Research Institute for Agriculture, Food and Environment, responds that he and his colleagues replaced the titanium dioxide–infused drinking water two to three times per week and that the bottles were shaken multiple times per day. So they weren’t concerned about excessive amounts collecting at the bottom of the bottle.
Kaminski and others are not convinced by this argument, and they are also perplexed by the fact that Houdeau and his colleagues used water as a test. “The irony around this is that it’s not how people are exposed to titanium dioxide,” he says. “We’re exposed to it in food.”
Joe Zagorski, a toxicologist at the Center for Research on Ingredient Safety at Michigan State University, says that it is critical to get the route of exposure correct in a study to be able to draw meaningful conclusions. “You have to ask, ‘Is this type of exposure even achievable in humans?’” he says. “Would it ever happen?”
In 2019 Kaminski and his colleagues published a replication of the 2017 study but added titanium dioxide to rats’ food instead of water. They did not find aberrant crypt foci or other indicators of toxicity in the animals. The scientists did get some industry support to do the research, but funders could not see the results until they were published in the peer-reviewed journal Food and Chemical Toxicology. And the researchers did not know which animals had been exposed to titanium dioxide until their analysis was complete.
Back in 1979 the National Cancer Institute also evaluated the potential toxicity of titanium dioxide in food in rats and mice, exposing them to large amounts of the chemical for two full years, which is most of a rat’s lifetime. They found no indication that titanium dioxide in food could cause cancer.
Why might the chemical be less toxic in food than in water? Recent work by nanotoxicology researcher Saji George of McGill University, published in the journal Nanoscale, has provided some insight. George’s lab discovered that proteins and other molecules found in food bind to titanium dioxide nanoparticles, encapsulating their surface, and this makes it harder for the particles to interact with cells and cause damage.
Houdeau says he and his colleagues are currently working on a new study looking at chronic exposure of titanium dioxide through food in mice and expect to publish later this year.
What about titanium dioxide in sunscreen?
Over the past few years, the FDA has evaluated 16 active ingredients in sunscreen, including titanium dioxide. In 2021 the agency concluded that the chemical and zinc oxide were safe and effective. (The other 14 ingredients required additional data to draw any conclusions or were outright unsafe, the FDA said.)
Are there better ways to evaluate titanium dioxide in food?
George says that studies evaluating the acute toxicity of titanium dioxide are important, but they’re not everything. “You’re missing other big parts of the picture,” he says. “There are so many other things that could be happening with small, consistent amounts of titanium dioxide in a diet over a long period of time.” For instance, George and his colleagues recently found that titanium dioxide—and nanoparticles more broadly—could be enhancing allergies to proteins in food. That result may not be as striking as a study mentioning the potential to cause cancer, but it could still be important for human health.
George also says that most toxicology studies only take into account the toxicological impact on healthy animals, which, again, isn’t the full picture. “We don’t know how titanium dioxide could enhance certain diseases—for example, inflammatory bowel disease in people with preexisting conditions,” he says.
Why did different countries come to different safety conclusions?
There are different approaches to weighing risk. To ban titanium dioxide in food, actual proof of increased risk is required by regulatory agencies in countries such as the U.S. This is also true in Canada, where a recent evaluation of scientific evidence led to the conclusion that titanium dioxide as a food additive is safe. In the E.U., however, uncertainty about safety—the inability to rule out potential harm—is enough to trigger regulatory action.
Although Oomen believes the E.U.’s cautious response to titanium dioxide is warranted, she says methods used to study the chemical need to be improved so they lead to more definitive conclusions about human health. For example, she notes, research should provide titanium dioxide in food in amounts comparable to what people would ingest.
Kaminski agrees that better research methods are needed, but—as of now—he is not worried. “I think that titanium dioxide in the amount that it’s used in Skittles and food products is of no toxicological concern or health concern to the public,” he says. “There’s just not the evidence to support that currently.”