Tartrazine and Other Azo Dyes: The Food Colours Linked to Hives

Azo dyes like tartrazine (E102) are bright synthetic food colours that can trigger hives and itching in sensitive people. A UK plain-English guide to what they are, who reacts, the label rules, and how to spot them.

What they are

Azo dyes are a family of synthetic colours used to make food and drink look bright and appealing. They are defined by a shared chemical feature called the azo bond, and they produce vivid yellows, oranges and reds. Tartrazine, listed as E102 or FD&C Yellow 5, is the best known, alongside colours such as sunset yellow (E110), carmoisine (E122) and ponceau 4R (E124).

They are popular with manufacturers because they are cheap, stable and intensely coloured, holding their shade through processing and storage far better than many natural alternatives. That is why they have historically appeared in such a wide range of sweets, drinks and packet foods. Their job is purely cosmetic: they change how a food looks, not how it tastes or how long it keeps.

Which foods it’s in

Azo dyes turn up wherever a strong, cheerful colour sells a product. Common homes include soft drinks and squashes, sweets and boiled confectionery, ice lollies and jellies, packet sauces and seasonings, savoury snacks, and some cakes and desserts. They also appear in some medicines and food supplements, where a colour is used to identify or brighten a tablet or syrup.

Their presence is not a sign of a “junk” food as such, and a product can look wholesome while still containing them. Equally, many everyday products no longer contain them at all, because a lot of UK manufacturers switched to natural colourings. The only way to know for a given product is to read the label.

The UK rules

In the UK, food colours are regulated additives and must be declared on the ingredients list of any prepacked food, by name or by E-number, with their function given as “colour”. An E-number is not a warning, it simply means the colour has been assessed and approved for use.

There is one important label rule for this group. Following research at the University of Southampton that raised questions about colours and children’s behaviour, six synthetic colours, the so-called “Southampton six”, carry a mandatory advisory in the UK and EU. Any food containing tartrazine (E102), quinoline yellow (E104), sunset yellow (E110), carmoisine (E122), ponceau 4R (E124) or allura red (E129) must state on the label that the colour “may have an adverse effect on activity and attention in children”. That warning is specifically about behaviour in children, not about skin, but it is genuinely useful to a sensitive adult too, because it flags at a glance that one of these azo-type colours is present. It was partly this measure, and consumer pressure that followed it, that led many UK brands to remove these colours voluntarily.

The skin connection

For most people azo dyes cause no problem at all. In a sensitive minority, though, they are linked with hives (urticaria), itching and the worsening of long-standing skin conditions such as eczema, sometimes several hours after eating. This is a skin response rather than a digestive one: the typical signs are raised itchy welts, flushing or an eczema flare, not an upset stomach.

The mechanism is usually not a true allergy. Azo dyes are thought to act as pseudo-allergens, provoking a histamine-type reaction without the immune system producing specific antibodies against them. That is why reactions tend to be dose-dependent, building up rather than striking instantly, and why they can be hard to pin down. People who already have chronic hives, or who are sensitive to aspirin, appear more likely to notice a reaction, which is a useful clue if either applies to you. Because it is intolerance rather than classic allergy, a small amount may be tolerated while a larger dose, or several coloured products in a day, tips things over.

How to spot it on a label

Scan the ingredients list for tartrazine, E102, Yellow 5 or FD&C Yellow 5, and for the other azo colours by name or E-number: sunset yellow (E110), carmoisine (E122), ponceau 4R (E124) and allura red (E129). They will be listed as a “colour”. On medicines and supplements the same names appear in the ingredients or excipients.

The “may have an adverse effect on activity and attention in children” statement is a quick secondary signal: if you see it, one of the six Southampton colours is present. It will not tell you which one without checking the list, but it tells you to look.

A balanced take on the evidence

It is worth being honest that the evidence here is mixed and the reactions are individual. Regulators consider azo dyes safe at permitted levels for the general population, and the Southampton research that prompted the label warning was about attention and activity in children, which is a different question from skin reactions in adults. Rigorous challenge studies of colour sensitivity in urticaria have produced varied results, and only a small proportion of people with chronic hives turn out to react to colours when tested carefully.

None of that changes the practical point for a sensitive person, which is simple: if your skin reacts, the average result does not matter, your own pattern does. So the balanced position avoids both extremes. There is no need for the whole population to fear azo dyes, and no need to strip them from a diet on principle, but for the minority who genuinely react, identifying and managing that trigger is entirely reasonable.

What to do if you suspect it triggers your skin

Start by tracking rather than cutting. Keep a short diary of what you eat and drink, including coloured sweets, squashes and medicines, and note when and how badly your skin flares. Because azo-dye reactions can be delayed and dose-dependent, record the quiet days as well as the bad ones, so a pattern has a chance to show.

If a colour does seem to be a trigger, take your diary to a professional rather than acting alone. A GP can advise and refer, a registered dietitian can help you avoid a specific colour without narrowing your diet unnecessarily, and an allergist can assess you if a clearer answer is needed. Any elimination should be short, targeted and ideally supervised. This page is educational information to support that conversation, not medical advice or a diagnosis, and persistent or severe hives always deserve a professional opinion.

Check products against your list

To check a packaged food, a free scanner like Yuka will give it a general health score and flag common additives by reputation. That is a useful broad read, but the score is the same for everyone, so a product can rate well and still contain the one colour your skin reacts to. Fig is excellent if you are managing a wider eating pattern such as low-histamine. To check a product against the specific additives that make your skin flare, a personal-list app like ClearaScan lets you save the colours and ingredients you react to once, then scan any product, food, medication, shampoo or cosmetic, and it flags only your triggers against your ingredient guard list. It also keeps a Reaction Journal so you can tie a flare back to the exact product that caused it, a shared Care Circle so family or carers can scan for you, and a Trusted Products list for items you have cleared. It is currently in early access. (Disclosure: our editor co-founded ClearaScan, and we are not paid to mention the others.)

Written and reviewed by the Sensitive Skin Lab editorial team.