From the Roman wonder-drug of, uh, cabbage, to the turn-of-the-century fad of Fletcherism, to today’s preoccupation with mostly-pointless vitamin pills, what we eat and how we eat it has long been an obsession for human societies. 

And few things get people worrying about what they’re putting in their bodies more than (gasp) artificial foods. Whether it’s the “frankenfood” panic of the 1990s, or the (and admittedly, they had a point here) deadly arsenic coloring in Victorian sweets, the idea that our food might be adulterated somehow – and that those adulterations are going to harm us and our children – is a stubborn and evidently evocative fear.

So it’s not from nowhere that, earlier this year, California governor Gavin Newsom signed the California School Food Safety Act, banning public schools in the state from serving or selling food containing any of six synthetic food dyes. But is the move scientifically justified? Should we all be trying to avoid artificial colorants in our diets? Or is this just another food-based panic?

Let’s see what the facts say.

Why has California banned some synthetic food dyes?

There are nine synthetic food dyes approved by the FDA, but only six – Blue 1, Blue 2, Green 3, Yellow 5, Yellow 6 and Red 40 – have been outlawed by the new School Safety Act.

Initially proposed in 2021 by California Assemblymember Jesse Gabriel, “the goal […] is to encourage companies to make minor modifications to products sold in California if they want their products to be sold in California public schools,” he told NBC News at the time.

But what prompted such a unilateral move? In his defense of the proposed bill, Gabriel pointed to a recent assessment on the dyes published by the state’s Office of Environmental Health Hazard Assessment (OEHHA): “We conducted a systematic literature search that identified numerous clinical trials examining neurological effects of food dyes in children,” the resulting paper noted; “we involved expert scientists and the general public […] and independent external expert scientists peer-reviewed the draft assessment before it was revised and released as this final report.”

This assessment, in turn, came after years of anecdotal and circumstantial evidence of some connection between the synthetic dyes and various health issues. Parents have long been told, whether correctly or not, that additives in food are worsening their kids’ ADHD or other behavioral issues, while some food dyes – such as Red 3, considered a carcinogen since the 1990s – are banned by the FDA for safety reasons in things like cosmetics, but not food. 

It’s a recipe for mistrust and confusion – which is one reason why the OEHHA determined a new review was required. Unfortunately for fans of brightly colored snacks, however, the results were pretty damning: “Overall, our review of human studies suggests that synthetic food dyes are associated with adverse neurobehavioral effects, such as inattentiveness, hyperactivity and restlessness in sensitive children,” the report concluded. 

“The evidence supports a relationship between food dye exposure and adverse behavioral outcomes in children, both with and without pre-existing behavioral disorders.”

Why haven’t other places banned synthetic food dyes?

But if the case is so cut-and-dry, you might ask, why are we only now banning these dangerous chemicals? And why only one state? Isn’t anybody else concerned about the health effects of these synthetic food dyes?

Well, in fact they are. Proponents of the dyes’ removal from US diets often point to EU food regulations as an example: many food dyes permitted in the US are outright banned in Europe, including Green 3 and titanium dioxide, one of the most widely used food pigments in the US common in coffee creamers, candy, and toothpaste. Other dyes are strictly regulated: Red 40, Yellow 5, and Yellow 6 may be used in food but only if accompanied by a warning label stating that the colorants “may have an adverse effect on activity and attention in children.” 

Even within the US, California is far from alone in its hesitancy over certain food dyes. In the last two years alone, the states of Washington, Missouri, New York and Illinois have all had their own bills introduced to ban similar selections of artificial dyes from being sold or used in food, with some lawmakers explicitly pointing to California as their inspiration. 

Okay, but what does the science say?

So far, the case against these synthetic food dyes seems pretty convincing – which raises an obvious question: why are they not banned at a federal level?

Well, it’s a combination of factors – but the overarching theme is a lack of evidence. 

That may seem a bold claim, given the wealth of studies, going back nearly half a century now, that have linked artificial food dyes to hyperactivity. Even the FDA itself, back in 2011, concluded that “for certain susceptible children with Attention Deficit/Hyperactivity Disorder and other problem behaviors […] their condition may be exacerbated by exposure to a number of substances in food, including, but not limited to, synthetic color additives.”

Here’s the problem, though: while there may be a reasonable amount of such evidence, many of the individual studies are flawed in some way. Perhaps they rely on parents’ reports of children’s behavior – notoriously biased – or maybe they studied dyes not available in the US. Most are small, or unrepresentative of US populations, and none found any particularly extreme effect.

And, ultimately, even the most convincing analyses can’t prove causality – that these artificial dyes are what definitively causes the behavioral changes apparently seen in the children who eat them. In fact, we don’t even know how such a causal link might even be possible – some researchers have suggested the neurotransmitter histamine may play a role; others think the dyes may act as neurotoxins in the brain. So far, however, no definitive mechanism has been found.

Unfortunately, the more evidence builds up against synthetic food dyes, the less likely that causal relationship is to be proved. 

“I think it’s been part of the problem with studies that have been out there, is that they can’t really separate out those dyes from those, basically, processed foods, or foods with a lot of sugar,” Sheela Sathyanarayana, a professor of pediatrics and environmental health sciences at the University of Washington and the Seattle Children’s Research Institute, told NBC in 2021.

But “we can’t ethically expose kids to a bunch of dyes and see what happens,” she added.

Until further evidence appears, however, it’s likely that these dyes will carry on being used in the US. The FDA’s policy is generally to consider substances “safe until proven harmful,” Joel Nigg, a professor of psychiatry at Oregon Health and Science University who performed a 2012 review of the link between synthetic food dyes and behavioral changes in children, told the New York Times in August this year – and currently, the agency maintains that no such proof has been demonstrated.

So, is there any good news? Well, potentially yes. With the new trend of states banning these food dyes, the FDA seems to be taking a few cues at last: “Over the past few years, there have been an increasing number of state bills to ban certain additives and set limits for certain contaminants,” an agency spokesperson told NBC in September. 

“The FDA must lead the way on food chemical safety,” they continued, “and under the new Human Foods Program, by instituting a systematic approach for chemical reassessment, the FDA is making the types of changes to our oversight program that will support equal access to safe foods, a resilient food supply, and maintain consumer confidence.”

Until any updated federal advice is issued – in either direction – it may also become easier to avoid synthetic dyes, even in states with no bans. Food companies are unlikely to create a California-legal version and a rest-of-the-US version of their products – and, after all, they have form here, often reformulating recipes to comply with EU regulations, but leaving the offending dyes in for the US market.

But here’s the ultimate question: no matter how easy or difficult it is, should we even bother avoiding these synthetic dyes? Ultimately, it’s a personal choice – but, Nigg pointed out, there’s really no downside to doing so.

“There’s a reasonable suspicion that food dyes may be harmful, at least for some kids,” he said. “So why expose them to it?”