Quick summary
At a glance
Red 40 is a synthetic food dye used to make foods and drinks look brighter. It provides no nutritional benefit.
Human research suggests synthetic food dyes can worsen hyperactivity, attention, or behavior in some children, although sensitivity varies and the evidence does not show that Red 40 causes ADHD. Newer animal and laboratory research has also raised questions about gut inflammation, microbiome changes, and DNA damage, but these effects have not been established in humans.
We choose to avoid Red 40 for both adults and children when practical, especially since it is primarily used for appearance and there are still unanswered questions about its long-term effects.
What it is
Red 40 is a synthetic food dye used to give foods, drinks, medications, supplements, and other products a red or reddish color.
It is an azo dye manufactured through chemical synthesis using raw materials derived from petroleum. Through a series of chemical reactions, these starting materials are converted into the finished color additive known as Allura Red AC. This doesn't mean Red 40 is literally petroleum—the final dye is a different chemical compound—but petroleum-derived materials are used in its production.
It can also be combined with other dyes to create colors that don't necessarily look red.
Why it is used
Red 40 is primarily used for appearance.
Manufacturers use it to make foods and drinks brighter and more visually appealing, create consistent colors between batches, restore color lost during processing, and produce red, pink, orange, or purple shades.
It does not provide nutritional benefits or make a food healthier.
Where it is commonly found
Red 40 may be found in:
Candy and gummies
Fruit snacks
Breakfast cereals
Sports and energy drinks
Soda and flavored beverages
Frostings and sprinkles
Gelatin desserts
Ice pops
Baked goods
Flavored dairy products
Chips and packaged snacks
Sauces and condiments
Children's medications and syrups
Vitamins and supplements
Toothpaste
Something does not necessarily have to look bright red to contain Red 40. It can be mixed with other dyes to create orange, purple, brown, and other shades.
What current research says
The strongest human evidence surrounding synthetic food dyes involves behavior and attention in children. Reviews of controlled studies have found that synthetic food dyes can worsen hyperactivity, attention, or other behavioral symptoms in some children, although sensitivity varies. Red 40 is one of the major dyes represented in this research, but many studies tested combinations of dyes rather than Red 40 alone. Because of this, the evidence does not show that Red 40 causes ADHD or that every child will react to it.
Beyond behavior, newer research has raised questions about gut health and inflammation. A 2022 Nature Communications study found that chronic exposure to Red 40 (Allura Red AC) increased susceptibility to experimental colitis in mice and affected intestinal serotonin, the gut microbiome, and intestinal barrier function. This is important research, but it has not established that the same effects occur in humans.
There are also emerging concerns about DNA damage. A 2023 study found evidence of DNA damage in laboratory-grown human colon cancer cells and in colon tissue from mice exposed to Red 40. The researchers also observed microbiome changes and low-grade intestinal inflammation in mice under certain experimental conditions. These findings warrant further research.
Researchers are now investigating whether these effects could have implications for long-term intestinal and colorectal health. A 2024 review in Carcinogenesis examined the emerging evidence involving Red 40, inflammation, microbiome disruption, DNA damage, and pathways potentially involved in colorectal cancer. At this point, however, there is not sufficient human evidence to conclude that Red 40 causes cancer, though we choose to avoid it either way.
Overall, the evidence is strongest for neurobehavioral effects from synthetic food dyes in a subset of children. The research involving gut inflammation, microbiome changes, and DNA damage is concerning but currently relies heavily on animal and laboratory studies. Research in adults and on long-term human exposure remains limited.
We choose to avoid it fully for both adults and children.
Potential concerns or controversies
Behavior & Attention in Children
Human research suggests synthetic food dyes can worsen hyperactivity, attention, or other behavioral symptoms in some children. Some children are affected worse than others, some not at all.
Gut Inflammation
Chronic Red 40 exposure increased susceptibility to experimental colitis in mice and affected intestinal pathways involving serotonin, the microbiome, and intestinal barrier function. Whether this occurs in humans at typical dietary exposures remains unknown.
Microbiome Changes
Animal research has reported changes in gut bacteria following certain Red 40 exposures. Researchers are still investigating whether similar changes occur in humans and whether they have meaningful health consequences.
DNA Damage
Laboratory and animal research has reported DNA damage associated with Red 40 exposure under experimental conditions. This is a legitimate reason for further investigation, but human dietary exposure has not been shown to cause the same effect.
Possible Long-Term Effects
Researchers are investigating whether chronic exposure could influence inflammatory or other biological pathways relevant to long-term disease. We currently don't have strong enough human evidence to know what long-term exposure means for adults or children.
Individual Sensitivity
The behavioral literature suggests that people—particularly children—may differ considerably in their sensitivity to synthetic food dyes.
Limited Adult Research
Much of the human research surrounding behavioral effects has focused on children. That means we have less direct human evidence about potential effects of long-term Red 40 exposure in adults.
Lack of evidence of harm in adults is not the same as evidence that harm occurs; it simply means this area is less well studied.
No Nutritional Benefit
Red 40 is primarily used to change the appearance of food.
For us, that matters when weighing potential risks against benefits: there isn't a nutritional reason we need to consume it.
Practical takeaway
We choose to avoid Red 40 for both adults and children.
The strongest human evidence of potential effects involves behavior and attention in some children. Research in adults is much more limited, particularly when it comes to long-term exposure.
At the same time, newer animal and laboratory research has raised additional questions about gut inflammation, the microbiome, and DNA damage. These findings have not established that Red 40 causes these effects in humans, but we believe they're worth paying attention to.
Because Red 40 provides no nutritional benefit and is primarily added for appearance, we don't see a compelling reason to regularly consume it when dye-free alternatives are readily available.
Our approach is simply to minimize unnecessary exposure—for adults and children alike—while continuing to follow the research.
Alternative or common names
- Red 40
- FD&C Red No. 40
- Allura Red AC
- E129
- CI 16035
Related Better Products
Sources and references
- California Office of Environmental Health Hazard Assessment (OEHHA) · 2021
Large evidence assessment examining human, animal, mechanistic, and exposure evidence for seven synthetic food dyes, including Red 40. It concluded that synthetic food dyes can contribute to adverse neurobehavioral effects in some children and that sensitivity varies between individuals.
- Environmental Health · 2022
Peer-reviewed review of human clinical trials and animal evidence examining synthetic food dyes and neurobehavior. The evidence indicates that some children may experience adverse behavioral effects, although many studies evaluated combinations of dyes rather than Red 40 alone.
- The Lancet · 2007
The Southampton study found that certain mixtures of artificial colors and sodium benzoate were associated with increased hyperactive behavior in children from the general population. Because mixtures were tested, the findings cannot be attributed specifically to Red 40.
- Neurotherapeutics · 2012
Review and meta-analysis examining artificial food colors and ADHD-related symptoms. It found evidence of a small behavioral effect overall and suggested that a subset of children may be particularly sensitive.
- Nature Communications · 2022
Mouse study finding that chronic Allura Red exposure increased susceptibility to experimental colitis through mechanisms involving intestinal serotonin and the gut microbiome. Intermittent exposure did not produce the same result under the study conditions, and whether these effects occur in humans remains unknown.
- Toxicology Reports · 2023
Laboratory and mouse research reporting DNA damage after Red 40 exposure. Longer-term mouse experiments also found microbiome changes and low-grade colonic inflammation under particular dietary conditions. These findings have not established the same effects in humans.
- Carcinogenesis · 2024
Review examining emerging evidence involving Red 40, DNA damage, inflammation, microbiome changes, and mechanisms potentially relevant to colorectal cancer. It argues that additional investigation is warranted but does not establish that Red 40 causes cancer in humans.