Synthetic food dyes — and their links to neurobehavioral issues in children — are having a moment.

Last month, California governor Gavin Newsom signed the California School Food Safety Act into law, banning the state’s public schools from serving or selling foods containing six synthetic food dyes starting in 2028. Earlier this month in Michigan, protests broke out in front of the Battle Creek headquarters of WK Kellogg Co., after the company drew renewed criticism for their broken commitment to remove synthetic food dyes in U.S. products, including cereals. 

Meanwhile, the same dyes banned in California are still approved by the U.S. Food and Drug Administration. The agency doesn’t appear to be changing course, maintaining that there isn’t sufficient evidence to prove that synthetic dyes cause issues like ADHD, hyperactivity or lack of focus. 

The list of foods containing synthetic food dyes is a long one. And fueling the uproar is the impossibility of discerning the risk a child has while consuming them. When federal and state guidelines aren’t aligned, it can be tricky to find out what foods contain the dyes and if they should be avoided altogether.

Despite limited evidence of a neurobehavioral connection, experts think some children are probably more susceptible than others. Many experts are adamant that California’s act ensures safety for the state’s public school students, and they hope the act could inspire other states to follow suit, forcing food manufacturers to reconfigure their recipes.

“I think it’s a great place to start because school is an environment where kids need to be able to focus. They need to be able to feel like they are in control of their bodies,” says Melanie Benesh, vice president of government affairs for the Environmental Working Group in Washington, D.C., a nonprofit corporation that cosponsored the California School Food Safety Act. “It creates a better learning environment for everyone.”

Amidst this national conversation, Science News looked at how we got to this point and what the science has to say about consuming synthetic food dyes.

What are synthetic food dyes and why are they in our food?

Synthetic dyes add color to food. Each one has a unique molecular structure that absorbs specific frequencies of light, allowing humans to perceive a rainbow of colors in otherwise bland snacks. Beyond adding a splash of color, synthetic dyes are essentially useless. They don’t help preserve food or add any nutritional value; their job is to entice.

“A lot of these foods are candies, cereals — things that are marketed to kids,” Benesh says. When manufacturers use synthetic dye, it “makes their food more brightly colored, more attractive to kids, and I think it helps them sell their products.” 

What products have synthetic dyes?

Foods with synthetic dyes aren’t packaged with a warning label in the United States, so sifting through individual product labels is the usually the only way to decipher exactly which food items contain which dyes. If present, synthetic dyes will be listed in the fine print of an item’s ingredients list, usually as the name of a color followed by a number (like “Yellow 5”). If you’re looking to avoid dyes, here are some grocery store staples to watch out for:

• Baked goods such as cake mix, sugar cookies and gingerbread
• Snack foods such as Pop-Tarts, Cheetos and even some dried fruits
• Candies such as M&M’s, Skittles and Nerds
• Cereals such as Froot Loops, Trix and Lucky Charms
• Beverages and specialty drinks such as Electrolit, Pedialyte and Powerade

It’s not just food products that contain synthetic food dyes. Some eyeshadows, hair products and medications contain some of the dyes now banned in California.

When did scientists realize that synthetic dyes might be harmful?

Synthetic dyes have a long and troubled history. Lead chromate, arsenic and additives made from coal tar were some of the first iterations, packing a poisonous punch for 19th and 20th century consumers. In 1950, dozens of children fell ill after consuming Halloween candy tainted with a dangerous dye, Orange 1 (SN: 8/12/11).

Many modern synthetic dyes were invented around the same time; five of the six dyes banned in California were FDA approved by 1931. But their potential for harm wasn’t widely discussed until the mid-1970s, when the idea of a potential link between food dye and childhood hyperactivity was set loose into the public, says Mari Golub, a developmental neurotoxicologist at the University of California, Davis. A flurry of research followed, but the FDA maintained their guidelines.

Still, some scientists say that associations are evident. Over the past 50 or so years, a growing body of scientific research and anecdotal evidence has pointed to a link between some synthetic food dyes and neurobehavioral issues in kids, which can present as volatile moods, hyperactivity and lack of focus.

So why did California ban the six synthetic dyes?

In 2021, California’s Office of Environmental Health Hazard Assessment released a report that would help push the state to ban Blue 1, Blue 2, Green 3, Red 40, Yellow 5 and Yellow 6 in public schools. 

The report’s authors scoured available research that investigated how synthetic food dyes affect children. They analyzed 25 clinical trial studies that compared periods of time when groups of children consumed foods colored by synthetic dyes to periods when they ate placebos. In many of the trials, parents and teachers noted any behavioral issues as they arose. The report authors eventually wrote that 16 of the studies showed a credible link between the behavioral outcomes and a child’s consumption of synthetic dyes.

But uncovering a link doesn’t mean that scientists can confirm that synthetic dyes are the direct cause of neurobehavioral issues. That’s where animal studies come in.

Research with rats, mice and the occasional rabbit have shown a clearer connection between individual synthetic food dyes and neurobehavioral effects. Some animals exposed to synthetic dyes, like the ones banned, can become hyperactive or exhibit signs of memory loss.

While animal studies can be important tools for comparison, the amount of food dye given to lab rats is difficult to compare to, say, how many Red 40–colored sprinkles are on a cupcake. It’s hard to tally the dye in individual sprinkles, chips and cookies across a child’s diet.

But animal studies have shown that dyes do influence animals neurologically, and they can help scientists determine which individual dyes and doses start to create negative effects, says Mark Miller, a pediatric environmental health physician at California’s Office of Environmental Health Hazard Assessment in Oakland who worked on the assessment.

Why was California’s decision controversial?

Not everyone is supportive of California’s ban.

“Consistency in food regulations across states and federal agencies is critical for ensuring public confidence,” says Sean Taylor, an organic and biological chemist with the International Association of Color Manufacturers in Washington, D.C. He notes that, the FDA reviewed the scientific literature like Golub’s team did and concluded there was no causal link between children consuming synthetic dyes and unwanted behaviors. 

It’s hard to be specific when talking about the danger of food dyes because there isn’t that much research out there to begin with. And technically, the FDA and California’s 2021 Health Assessment don’t contradict each other: One finds no causal relationship; the latter finds an associative link. 

Because there hasn’t been a study comparing one group of children with a food-dye-free diet to another group of children consuming food concentrated with individual doses of synthetic dyes, it’s difficult to identify a causal relationship.

“We don’t have the kind of data that would be gold standard causal data,” says Amy Gilson, the Deputy Director for External and Legislative Affairs at California’s Office of Environmental Health Hazard Assessment in Sacramento. It’s unlikely that a black-and-white study will ever be published. But, Gilson says, “you don’t need to have all the causal data that anyone would ever want to say, ‘Hey, you know there’s good evidence here. There’s good science that points us to needing to take some action.’”