How-to guide

How to Find Azo Dyes on a Label

Azo dyes are the food colours most linked to hives. The exact names and E-numbers to scan for, plus the children's-warning shortcut that flags them in two seconds.

Why azo dyes get singled out

Of all the food colours, the synthetic azo dyes are the ones most consistently linked to hives, itching and worsening urticaria in sensitive people. Spotting them quickly is one of the most useful label skills for skin-sensitive shoppers.

Step 1: Memorise the core azo list

The main azo colours to know are tartrazine (E102), Sunset Yellow (E110), carmoisine/azorubine (E122), Ponceau 4R (E124), Allura Red AC (E129) and amaranth (E123). Quinoline Yellow (E104) is often grouped with them as a Southampton colour, though it is technically a different chemical family.

Step 2: Scan the colours in the ingredients

You do not need to read the whole list, just run your eye over the colours and match them against your azo list, by name or by E-number. They are usually grouped near the end of the ingredients.

Step 3: Use the children’s warning as a shortcut

In the UK and EU, products containing the main azo colours must carry “may have an adverse effect on activity and attention in children”. If you see it, azo colours are present; if a product does not carry it, it is free of those particular colours. It is the fastest screen there is.

Step 4: Check coatings and medicines too

Azo dyes are used to colour tablet and capsule coatings, supplements and some toothpastes, not just food. If a reaction does not match anything you ate, check those.

A few extra tips

Green and orange products are often blends, so a green sweet may contain a blue plus a yellow azo dye. And remember azo dyes cross-react, so if one bothers you, screen for the whole group rather than just the one.

Check it against your own list

A free database like Open Food Facts lets you look up a product’s colours, and Fig is genuinely good for managing a defined eating pattern. These give broad information rather than a check against your own skin. To do it automatically, a personal-list app like ClearaScan lets you save the azo colours (and your other triggers) once and scan any product, food, medication or cosmetic, against your ingredient guard list, flagging only yours. Its Reaction Journal lets you tie a flare back to the product that caused it, a shared Care Circle lets family scan for you, and a Trusted Products list keeps what you have cleared. It is currently in early access. (Disclosure: our editor co-founded ClearaScan, and we are not paid to mention the others.)

More how-to guides

How to Introduce a New Product Without Triggering a Flare

Adding products one at a time is the simplest way to protect reactive skin and pinpoint problems. The safe way to bring in a new cleanser, serum or active, step by step.

How to Keep a Food-and-Skin Diary

A simple log of meals and flares is the fastest, cheapest way to spot your own skin triggers, especially the slow, delayed ones. How to keep one that actually reveals the pattern.

How to Patch-Test a Hair Dye Before You Colour

Permanent hair dye is a common cause of severe scalp and face reactions. A proper allergy alert test before every colour can catch trouble early. Here is how to do one.

How to Patch-Test a New Skincare Product at Home

A simple at-home patch test can catch a reaction before it reaches your face. How to do one properly, how long to wait, and what it can and cannot tell you.

The Sensitive Skin Ingredient Decoder

A free one-page guide to reading a skincare label fast: the irritants to watch, the fragrance loopholes, and what "fragrance-free" and "hypoallergenic" really mean.

No spam, just the guide and the occasional new article. Unsubscribe anytime.

Common questions

Is Brilliant Blue an azo dye?

No, it is a triarylmethane dye. Avoid grouping it with the azos; it is a separate, generally lower-concern colour.

Are azo dyes banned?

No, they are permitted within limits in the UK and EU, but they carry the children's warning label.

Written and reviewed by the Sensitive Skin Lab editorial team.

A note on this content. The Sensitive Skin Lab publishes general educational information, not medical advice. If you suspect you have an allergy or sensitivity, consult a qualified dermatologist or allergist. Product formulations and labels change without notice, so always check the ingredients on the product itself.