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. Here is what they are, who reacts, and how to spot them.
What they are
Azo dyes are a family of synthetic colours used to make food and drink look bright. 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 cheap, stable and vivid, which is why they appear in so many sweets, drinks and packet foods.
Who tends to react, and how it shows on the skin
For most people azo dyes cause no problem. In a minority, though, they are linked to hives (urticaria), itching and worsening of long-standing skin conditions, sometimes hours after eating. People who already have chronic hives or who are sensitive to aspirin are more likely to notice a reaction. This is a skin response, not a digestive one: the typical signs are raised itchy welts, flushing or an eczema flare rather than an upset stomach.
The honest take
The evidence is mixed and reactions are individual. Regulators consider azo dyes safe at permitted levels for the general population, and in the UK many manufacturers removed them voluntarily after the Southampton studies raised questions about children. The practical point for a sensitive person is simple: if your skin reacts, it does not matter what the average response is, what matters is your own.
Where they hide
Soft drinks and squashes, sweets, ice lollies, packet sauces, snack foods, and some medicines and supplements. On the label look for Tartrazine, E102, Yellow 5, or the other azo colours by their E-numbers (E110, E122, E124, E129).
Check it against your own triggers
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.)