Red 40 is made from petroleum. Specifically, it’s synthesized from petroleum-derived chemical building blocks through a series of reactions in a lab. Despite its presence in everything from candy to sports drinks, there’s nothing fruit-based or natural about its vivid red color.
The Chemical Building Blocks
Red 40’s formal name is Allura Red AC, and its production starts with compounds extracted from crude oil. The synthesis, first described in a 1970 US patent by chemists at Allied Chemical, involves coupling two petroleum-derived intermediates: a modified form of sulfanilic acid and a compound called 2-naphthol-6-sodium sulfonate. That basic method, now over 50 years old, is still used today.
The reaction that gives Red 40 its color is called azo coupling. It creates a nitrogen-nitrogen double bond (an “azo bond”) at the center of the molecule, and this bond is what absorbs light in a way that makes the dye appear bright red. The final product is a dark red powder that dissolves easily in water, which is why it works so well in liquids like sodas and sports drinks. A variation called “Red 40 Lake” is designed not to dissolve, making it useful for coloring solid foods, coatings, and cosmetics.
Where You’ll Find It
Red 40 is the most widely used artificial food dye in the United States. It shows up in a surprisingly broad range of products: energy and sports drinks, sodas, cereals, candy, chewing gum, gelatin desserts, dairy products like flavored yogurt, protein powders, and baked goods. It’s also common in medications and cosmetics.
On ingredient labels, Red 40 goes by many names depending on where the product was made. You might see it listed as FD&C Red No. 40, Allura Red AC, CI Food Red 17, E129, or INS No. 129. The “Lake” versions (Red 40 Lake or FD&C Red No. 40 Aluminum Lake) refer to the water-insoluble form. All of these names refer to the same synthetic dye.
What Happens to It in Your Body
Your body doesn’t absorb Red 40 the way it absorbs nutrients. Most of it passes through your digestive tract, but along the way, gut bacteria break it apart. Research published in the journal Cell Metabolism identified specific intestinal bacteria, including Bacteroides ovatus and Enterococcus faecalis, that split Red 40’s azo bond. This produces a metabolite called 1-amino-2-naphthol-6-sulfonate sodium salt (often abbreviated ANSA-Na).
That metabolite has drawn scientific attention. In a 2021 mouse study, ANSA-Na promoted intestinal inflammation in animals that were already genetically predisposed to colitis. The inflammation depended on having gut bacteria present to break the dye down in the first place. This doesn’t mean Red 40 causes gut disease in healthy people, but it raises questions about whether the dye could be a problem for individuals with existing inflammatory bowel conditions.
The Debate Over Behavior in Children
The most persistent concern about Red 40 is whether it contributes to hyperactivity in children. The FDA convened an advisory committee in 2011 to review the evidence and concluded that a causal link between synthetic food dyes and behavioral effects had not been established. The agency has continued monitoring new research since then, reviewing multiple meta-analyses and clinical trials published through 2017.
The findings are mixed but lean toward a small effect. A 2017 systematic review by Pelsser and colleagues found that diets free of artificial food colors had a “small to medium” effect size on ADHD symptoms. That’s enough to be measurable in studies but not enough for the authors to recommend dye-free diets as a general treatment for ADHD. Some children do appear more sensitive to food dyes than others, but identifying which children will react, and to which dyes, remains difficult.
The European Union took a more cautious approach. Products sold in the EU that contain Red 40 (or any of five other synthetic dyes) must carry a warning label stating the product “may have an adverse effect on activity and attention in children.” This label requirement has led many European manufacturers to reformulate their products with natural colorants instead. The same products are often sold in the US with Red 40 and no warning.
How to Spot and Avoid It
If you want to avoid Red 40, check ingredient lists for any of its alternate names: Red 40, FD&C Red No. 40, Allura Red AC, E129, INS No. 129, or any version with “Lake” in the name. US manufacturers are required to list certified color additives by name on the label, so it won’t be hidden under vague terms like “artificial color.” They are not, however, required to disclose how much of the dye a product contains, only to list ingredients in order of weight.
Products colored with beet juice, paprika extract, or other plant-based alternatives will typically say so on the label. These are becoming more common in the US as consumer demand shifts, though they tend to be less vivid and more expensive than synthetic options.