Red Dye 40 (also known as Red 40) is the most widely used synthetic food coloring used in the United States. More than 36,000 American food products — including candies, sodas, and cereals — contain this dye.
The U.S. Food and Drug Administration (FDA) approved Red Dye 40 for use in food in 1971, but has not reevaluated it for health risks in years even as consumer advocacy groups have voiced concerns.
In the fall of 2024, the state of California led the nation by enacting the first ban of Red 40 along with five other dyes in foods served in public schools.
Robert F. Kennedy Jr., President Donald Trump’s pick for U.S. Health and Human Services secretary, has also vowed to crack down on food dyes such as Red 40.
Even more scrutiny has been directed at Red 40 after the FDA banned the use of Red Dye 30 in foods and ingested drugs in January 2025.
With health concerns swirling around the food dye, here’s what you need to know about this synthetic ingredient.
As with all food colorings, Red Dye 40 is added to foods, drugs, and cosmetics in order to make these products more attractive, appealing, appetizing, or easily identifiable.
Companies use synthetic dyes rather than natural ones because they can be mass-produced at a fraction of the cost of gathering and processing natural materials.
Red Dye 40 is derived from petroleum or crude oil, and treated with other chemicals in a process to make it ingestible.
While ingesting small amounts of Red Dye 40 seems unlikely to affect overall health, a growing body of research suggests it may be connected with a number of issues.
Behavioral Issues in Children
Some research has linked Red 40 to increased hyperactivity and behavioral changes in some children, particularly those diagnosed with ADHD (attention deficit hyperactivity disorder), potentially worsening symptoms like difficulty sitting still, excessive talking, anxiety, moodiness, and irritability.
Countries in the European Union require foods containing Red 40 and other synthetic dyes to carry a warning saying that these products “may have an adverse effect on activity and behavior in children.”
"There's pretty good evidence at this point indicating a small but significant deleterious effect of Red 40 on the behavior of most children,” says L. Eugene Arnold, MD, a professor of psychiatry and behavioral health at the Ohio State University, who has conducted research on this topic.
Trials in Britain have linked juices containing dye to a small but significant rise in hyperactivity in children, with or without ADHD.
A review of 27 studies looking at artificial dyes, including Red 40, concluded that evidence “supports a relationship between food dye exposure and adverse behavioral outcomes in children.”
Allergic Reactions
According to Dr. Arnold, research has identified three genes that may direct the body’s reaction to synthetic dyes. One gene is involved in the synthesis of dopamine, a molecule that promotes focus and impulse control; the two other genes are involved in the synthesis of histamine, a molecule that promotes alertness.
The Center for Science in the Public Interest says that Red 40 may trigger allergic reactions in some people, causing hives and facial swelling.
Cancer
“Red Dye 40 is generally considered safer than the now-banned Red Dye 3, since it has not been shown to cause cancer in animals like Red 3 did with thyroid tumors,” says Lorne Hofseth, PhD, an associate dean for research with the Drug Discovery and Biomedical Sciences College of Pharmacy at the University of South Carolina in Columbia, who has conducted extensive research on artificial dyes.
Still, it’s known that Red 40 can contain trace amounts of benzene and 4-aminobiphenyl, which are known human carcinogens.
“Concerns about Red 40’s potential for accelerating cancer through DNA damage and inflammatory mechanisms suggest it may not be entirely risk-free,” Dr. Hofseth says.
Hofseth explains that synthetic dyes by their nature have the potential to result in inflammation.
“Synthetic food dyes are, by definition, xenobiotic, or foreign to the body,” he says. “Things that are foreign to the body are going to stimulate an inflammatory immune response and cause damage to cells.” Long-term inflammation and cancer are “intimately” connected, he says.
Hofseth and his collaborators conducted research on mice injected with the equivalent of an “acceptable” human daily intake of Red 40, and observed a low level of inflammation in the rodents’ colons after nine months.
They also looked at human colon cells exposed to Red 40 and saw DNA damage that increased as the dose of Red 40 increased.
Still, a dearth of research involving human subjects makes it difficult to know if results from animal and cell studies predict real-life cancer risk in people.
“The evidence for a cancer connection is suggestive but not conclusive — animal studies and cell research provide ‘pretty good’ evidence, but robust human studies are still needed to confirm the link,” Hofseth says.
Red Dye 40 has a number of different names that may appear on an ingredient list, including:
Allura Red AC
Red 40 Lake
Red 40
FD&C Red No. 40
FD&C Red No. 40 Aluminum Lake
Many foods that commonly include Red 40 have the bright color one would associate with the dye:
Pastries
Cakes and frosting
Cereals (such as Froot Loops, Lucky Charms, Trix, Fruity Pebbles)
Candy and gum (such as M&Ms, Skittles, Jolly Rancher, Starburst, Bubblicious)
Yogurt
Puddings
Gelatins
Ice cream
Popsicles
Soda and soft drinks (such as Hi-C, Code Red Mountain Dew, and Minute Maid Orange Soda)
Sports drinks
Energy drinks
Protein powders
Chips and salty snack foods (such as Nacho Cheese Doritos, Planters Cheez Balls, and Combos Pizzeria Pretzels)
The coloring can also be found in barbecue sauces, bouillon cubes, packaged fruit salads, and certain cereal bars.
Red 40 is not only found in many items that are bright red, but in some products with different colors, such as pickled ginger and wasabi-covered peas.
Certain medications and vitamins also use Red 40 to enhance appearance and provide brand identity. Dyes may be used to associate the visual appearance with the appropriate flavor in products like cherry-flavored children’s cough syrup, for instance.
The synthetic pigment is also found in a range of cosmetics, nail treatment, soaps, and skin care products, including lipstick, eyeliner, eyeshadow, blush, bubble baths, and even some kids’ toothpastes.
The best way to avoid Red Dye 40: “Read the labels of the food products you buy,” says Dr. Arnold. “The FDA requires food manufacturers to list all ingredients on the label, including dyes.”
He suggests that products may be healthier if they have coloring from natural sources, such as beets, turmeric, paprika, matcha, strawberries, and saffron, for example.
Arnold adds that parents may want to steer their children away from foods containing synthetic coloring, especially if they have an anxiety disorder or ADHD.
Red Dye 40 in small amounts is unlikely to harm most people, and the FDA permits it in food and regulates its safe use.
Still, some studies indicate that the dye may worsen behavioral issues in some children, and studies involving mice and human cells suggests a potential link to cancer, requiring more research to confirm.
To limit intake of Red Dye 40, avoid products containing these artificial pigments by checking product labels.
