Is Red Dye 40 bad for you?

What the research found

The study that changed the regulatory picture is the Southampton trial, published in The Lancet in 2007. Children from the general population — not a clinical ADHD group — were given drinks containing mixtures of six artificial colours plus the preservative sodium benzoate, and showed measurably increased hyperactive behaviour compared with placebo.

Two caveats belong with that result, and honest coverage includes them. The effect was found for mixtures, so it cannot be pinned on Red 40 individually. And the average effect size was modest, with wide variation between children — consistent with a subgroup being sensitive rather than every child being affected.

California's Office of Environmental Health Hazard Assessment reviewed the field in 2021 and concluded that synthetic food dyes can affect behaviour in some children, and that the levels children are exposed to today are higher than the levels the original safety assessments assumed.

Why the EU and US labels differ

Both regions permit the dye. The EU requires the activity-and-attention warning on the package under its food additives regulation; the US does not, and the FDA has maintained that the general evidence does not establish a causal link for children overall, while acknowledging that some children may be affected.

That gap is the single most useful thing to know about Red 40: the same product sold on both sides of the Atlantic can carry a behavioural warning in one market and nothing in the other. Manufacturers frequently reformulate for the EU with paprika extract, beetroot or anthocyanins rather than carry the label.

The direction of travel in the US is toward fewer synthetic dyes. California's School Food Safety Act, signed in 2024, bars several dyes including Red 40 from food served in public schools from 2027, and in 2025 federal regulators announced a push to move manufacturers off petroleum-based dyes voluntarily.

Red Dye 40 is not Red Dye 3

These are different chemicals with different histories, and conflating them is the most common error in coverage of this topic. Red Dye 3 (erythrosine, E127) caused thyroid tumours in rats, was removed from US cosmetics in 1990, and had its food authorisation revoked by the FDA in January 2025 under the Delaney clause.

Red Dye 40 has not been through that. It has never been shown to cause cancer in the animal studies used for approval, and the concern attached to it is behavioural. If you read that 'the FDA banned red dye', it was Red 3.

Where it turns up

Red 40 is the most-used colour in the American food supply and it is not confined to obviously red products. Beyond sweets, sports drinks, cereals and ice lollies, it appears in barbecue sauces, seasoned snack foods, some breads, flavoured yoghurts, and many children's medicines.

On a label it can read as Red 40, Red 40 Lake, FD&C Red No. 40, Allura Red AC, E129, or in the EU simply as a colour name with the E-number. Olive Detective matches all of those to a single flag, so the American and European spellings of the same product resolve identically.