Food Dyes and Your Health: What the Science Actually Says
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What synthetic food dyes actually are
The yellow number five study that shocked researchers
During the Huberman Lab audience questions session, someone asked Dr Shanna Swan about food dyes generally. She mentioned a recent study covered by Science magazine, one of the most prestigious scientific journals in the world, that she found remarkable enough to send to Joe Rogan.
The study in question found that a common yellow food dye, when applied to the skin of adult mice, made them translucent. You could see their organs through their skin. The mechanism involves the dye interacting with biological tissue in a way that changes how light passes through it.
That specific finding is about optical effects rather than toxicity, but it prompted a wider question worth answering properly: what do we actually know about synthetic food dyes and should we be avoiding them?
What Synthetic Food Dyes Actually Are
Synthetic food dyes are petroleum derived chemical compounds used to give processed foods consistent, bright colours that would not occur naturally. They have been in widespread use since the early twentieth century and are found in everything from fizzy drinks and sweets to breakfast cereals, sauces, medications and vitamins.
In the EU and UK, approved synthetic dyes are identified by E numbers on ingredient labels, E102 for tartrazine, the yellow dye also known as yellow number five in the US, E110 for sunset yellow, E122 for carmoisine, E124 for ponceau 4R, E129 for allura red and E133 for brilliant blue among others.
The Yellow Number Five Study That Shocked Researchers
The study Dr Swan referenced was published in Science magazine in 2024 by researchers at Stanford University and the University of Texas. They found that tartrazine, yellow number five, when applied topically to the skin of mice, temporarily rendered the tissue translucent, allowing organs and internal structures to be seen through the skin.
The mechanism involves the dye reducing what physicists call the scattering of light through biological tissue. The finding has genuine scientific interest for medical imaging and surgical applications, since being able to see organs non-invasively has obvious value.
It is important to be clear about what this study does and does not show. The finding was about optical effects in topical application, not about what happens when you eat tartrazine. The authors themselves did not frame it as a toxicity study and drew no conclusions about the safety of consuming it. The reason Dr Swan found it remarkable, and the reason it spread widely, is that it visually demonstrates how dramatically a synthetic dye can interact with biological tissue, which raises reasonable questions even if it does not answer them directly.
Which Dyes Are Most Concerning and Why
The evidence base on synthetic food dyes and health is genuinely mixed, which is worth being honest about rather than overstating in either direction.
The most consistent finding across multiple studies is a link between certain synthetic dyes and hyperactivity in children, particularly tartrazine, sunset yellow, carmoisine and allura red. A 2007 study published in The Lancet, one of the most respected medical journals in the world, found that a mixture of these dyes alongside the preservative sodium benzoate increased hyperactivity in children aged three and eight to nine. Following this study, the EU required foods containing these six dyes to carry a warning label stating the product may have an adverse effect on activity and attention in children. The UK Food Standards Agency subsequently recommended that manufacturers voluntarily remove these dyes, which many did.
Some synthetic dyes have also been associated with allergic reactions and intolerance in sensitive individuals, including tartrazine which is known to trigger reactions in some people with aspirin sensitivity.
The endocrine disrupting potential of synthetic food dyes is less well studied than that of pesticides, phthalates and PFAS. Some animal studies have raised concerns but the human evidence is currently limited. The precautionary principle suggests that petroleum derived compounds with demonstrated biological activity, which is precisely what the transparency study shows tartrazine has, are worth avoiding where practical.
How to Avoid Them Practically
Avoiding synthetic food dyes is largely a matter of avoiding heavily processed foods, which aligns with the broader guidance on the Food and Nutrition page anyway. The foods most likely to contain synthetic dyes are confectionery, fizzy drinks, brightly coloured snacks, some breakfast cereals, flavoured yogurts and processed sauces.
The six dyes that carry EU warning labels are E102, E104, E110, E122, E124 and E129. These are the ones with the strongest evidence for adverse effects in children and the most reason for general caution.
Natural food colours derived from plants, including beetroot red, turmeric yellow, spirulina blue and paprika extract, are widely used in cleaner food products and carry none of the concerns associated with petroleum derived dyes.
The evidence for adverse effects on attention and behaviour is strongest in children. Brightly coloured sweets, drinks and snacks marketed to children are where synthetic dye exposure is typically highest.
Related reading: our Food and Nutrition page covers the broader picture of what to look for and avoid in everyday food choices.
Sources: Yao et al., Science (2024) : tartrazine tissue transparency study | McCann et al., The Lancet (2007) : artificial colours and hyperactivity in children | European Food Safety Authority food colour re-evaluation programme | UK Food Standards Agency artificial colours advice