Red food coloring isn’t a single substance, and whether it’s harmful depends on which one you’re consuming and how much. The U.S. currently permits three synthetic red dyes in food: Red No. 3, Red No. 40, and Citrus Red No. 2 (used only on orange peels). Of these, Red No. 3 is being pulled from the food supply after the FDA confirmed it causes cancer in lab animals, and Red No. 40 faces growing scrutiny over links to behavioral changes in children and gut inflammation.
Red No. 3 and the Cancer Question
Red No. 3, also called erythrosine, has been on regulators’ radar for decades. Back in 1990, the FDA denied its use in cosmetics and topical drugs because studies showed it caused thyroid tumors in male rats exposed to high doses. The agency cited the Delaney Clause, a legal provision that prohibits any food additive shown to cause cancer in animals, regardless of dose. In 1992, the FDA announced its intention to do the same for food and ingested drugs but never followed through.
That changed recently. After reviewing data from a 2022 petition, the FDA determined that Red No. 3 causes cancer in male rats through a hormonal mechanism specific to rat biology. While the relevance to humans is debated, the Delaney Clause doesn’t allow for that distinction. The FDA has now moved to revoke authorization for Red No. 3 in food and ingested drugs. You’ll still find it in candy, cakes, cupcakes, cookies, frozen desserts, frostings, and some medications until manufacturers reformulate, but it’s on its way out.
Red No. 40 and Children’s Behavior
Red No. 40 (allura red) is by far the most widely used red dye in the American food supply, and the research here centers on hyperactivity in children. A well-known British study tested preschoolers with drink mixes containing several artificial colors, including Red No. 40. On analysis of children who followed the protocol closely, both the lower and higher dose mixes produced a statistically significant increase in hyperactivity scores compared to placebo. The effect size was small, ranging from 0.12 to 0.2.
A broader meta-analysis of 24 double-blind, placebo-controlled studies found a pooled effect size of 0.18 for parent-reported hyperactivity, dropping to 0.12 after adjusting for potential publication bias. To put that in perspective, an effect size of 0.12 is subtle enough that most parents wouldn’t notice it in an individual child. But across a population of millions of children consuming these dyes daily, even a small shift can be meaningful. These studies also tested dye mixtures rather than Red No. 40 in isolation, making it hard to pin the effect on any single color.
The FDA’s current acceptable daily intake for Red No. 40 is 7 milligrams per kilogram of body weight. For a 44-pound child, that works out to about 140 mg per day. Whether typical diets approach that threshold depends heavily on what a child eats, since Red No. 40 appears in everything from fruit snacks and sports drinks to flavored yogurt and cereal.
Gut Inflammation and Red No. 40
Animal research has raised concerns about what Red No. 40 does to the digestive system over time. In a study that exposed mice to Red No. 40 for ten months, the dye combined with a high-fat diet led to low-grade inflammation in the distal colon and rectum, along with significant shifts in gut bacteria. Specifically, the combination reduced beneficial bacterial communities while increasing populations linked to poor gut health. Mice on the high-fat diet with Red No. 40 showed lower diversity of microbial communities overall.
Interestingly, Red No. 40 alone (without the high-fat diet) didn’t significantly reduce overall bacterial diversity, but it did lower levels of one beneficial bacterial group on its own, and it still increased colon inflammation to a degree. Multiple studies have now demonstrated that chronic exposure to Red No. 40 provokes mild colitis in experimental settings. The same study also found that Red No. 40 caused DNA damage both in lab dishes and in living animals.
These are mouse studies, not human trials, so they don’t prove the same thing happens in people. But they do suggest that the combination of a typical Western diet (high in fat and processed food) with regular Red No. 40 consumption could stress the gut in ways that aren’t yet fully understood.
Natural Red Dyes Aren’t Risk-Free
If you’re switching to products labeled with “natural colors,” it’s worth knowing that the most common natural red colorant, carmine, carries its own risks. Carmine comes from cochineal insects and is used widely in yogurt, juices, and cosmetics. In a study of patients with chronic hives who underwent oral challenges with carmine, 8% tested positive for a carmine allergy. Reactions ranged from facial redness and itching within minutes to full-body hives, tongue swelling, difficulty breathing, and stomach disturbance.
Beet juice is another popular replacement, but it has practical limitations. The red pigments in beet juice degrade with heat and time, especially at temperatures above 25°C (77°F). That means beet-colored products can fade or turn brown during baking, cooking, or extended shelf storage. This is one reason manufacturers have been slow to replace synthetic dyes in baked goods and shelf-stable snacks: natural alternatives simply don’t hold up as well during processing.
How to Reduce Your Exposure
Ingredient labels are your most reliable tool. Red No. 40 appears as “Red 40,” “Allura Red,” or “FD&C Red No. 40.” Red No. 3 shows up as “Red 3,” “Erythrosine,” or “FD&C Red No. 3.” Both can appear in products you wouldn’t expect to be dyed, including white-frosted cakes (where small amounts adjust the shade), flavored medications, and some pickled foods.
If you’re concerned about children’s behavior, reducing artificial food dyes is a low-cost, low-risk change. The European Union has required warning labels on foods containing Red No. 40 and five other dyes since 2010, stating they “may have an adverse effect on activity and attention in children.” Many European manufacturers reformulated with natural colors rather than carry the label, which is why the same brand of candy or cereal often uses different colorants depending on whether it’s sold in the U.S. or Europe.
For adults without specific sensitivities, occasional exposure to Red No. 40 at levels within the established daily intake is unlikely to cause noticeable harm. The concern is cumulative, chronic exposure, particularly for children, people with inflammatory bowel conditions, and those eating heavily processed diets where synthetic dyes show up in nearly every meal.