Is Red 40 bad for you?
Yes, Red 40 is one of the additives worth limiting. The bright red synthetic dye sold as Red 40 in the US. One of the six colours the EU makes carry a children's activity-and-attention warning. European brands often colour the same product with beet juice instead.
Is Red 40 actually harmful?
One of the Southampton Six: in controlled trials, children given dye mixtures containing it at realistic supermarket doses showed more hyperactive, inattentive behaviour. The effect is dose-dependent and reverses when you cut it out, and it lands hardest on children — some parents notice a change within a week. There is no known benefit to offset it; the dye does nothing but colour.
What do regulators say?
EU labels must carry the "may have an adverse effect on activity and attention in children" warning. EFSA kept an acceptable daily intake of 7 mg per kg of body weight per day in 2009. The FDA still permits it as Red 40 with no warning, though in April 2025 it asked manufacturers to remove it and the other petroleum dyes voluntarily by the end of 2026, and California bans it from school food from the end of 2027.
Source: EU Regulation 1333/2008 (Annex V warning list) ↗So should you avoid it?
Known or suspected to cause harm: a substance EFSA or another regulator has flagged, or one restricted in some jurisdictions. Best kept out of a regular diet.
For the full reference on Red 40, including what it is and where it turns up, see the E129 page. Or scan a product and Yuzu tells you if it's inside.