Brilliant Blue (E133): The Synthetic Blue Dye and the Skin

Brilliant Blue (E133) is a synthetic blue colour in drinks, sweets and even mouthwash. Reactions are less common than with azo dyes, but they happen. What it is, where it hides on UK labels, and calm steps if you suspect a reaction.

What Brilliant Blue (E133) is

Brilliant Blue is a synthetic blue food colour, known as Brilliant Blue FCF, its European number E133, or in the United States as FD&C Blue 1 (often shortened to Blue 1). It belongs to the triarylmethane family of dyes, which is a genuinely important detail: much of the concern about food colours focuses on azo dyes specifically, and Brilliant Blue is not an azo dye. That makes it a lower-concern option in several respects, though it is still a synthetic colour that many sensitive shoppers choose to avoid.

Its job is purely cosmetic. It gives a clean, vivid blue and is very often blended with a yellow colour to produce green, which is why it turns up in far more products than the word “blue” on the front would suggest.

Which foods it is in

Brilliant Blue appears wherever a bright blue or green is wanted. Common places to find it include:

• Blue and green sweets, jellies and lollipops
• Ice pops, slushies and frozen treats
• Sports and energy drinks
• Blue mixers and cocktail syrups
• Some tinned processed peas, to boost the green
• Icing, sprinkles and cake decorations
• Non-food items such as mouthwash, toothpaste and some medicines

That non-food presence is easy to forget. If you are hunting a persistent reaction and the food diary comes up blank, a coloured mouthwash or medicine is worth a second look.

The UK rules

Under UK food labelling law, colours must be declared in the ingredients list, either by name or by their E-number, alongside the word telling you what they do, so you will see “colour: Brilliant Blue” or “colour (E133)”. This applies to pre-packed food sold in the UK.

Unlike the six Southampton colours (tartrazine, quinoline yellow, Sunset Yellow, carmoisine, Ponceau 4R and Allura Red), Brilliant Blue does not have to carry the Food Standards Agency statement that a food “may have an adverse effect on activity and attention in children”. That mandatory warning is specific to those six azo and related dyes. Brilliant Blue is a permitted colour used within set limits and is assessed as safe for the general population at those levels.

The skin connection

Reactions to Brilliant Blue appear to be less common than to the azo colours, but they do happen and are reported in the literature: hives, itching and flushing in sensitive individuals, usually as a pseudo-allergic response rather than a true allergy. People with chronic urticaria who react to a range of additives may find Brilliant Blue is one of several that contribute, rather than a standalone trigger.

As with other synthetic colours, standard allergy tests generally look normal, because the mechanism is not the classic antibody-driven one those tests detect. True allergy to Brilliant Blue is uncommon. Intolerance, where the skin reacts without a formal allergy, is the more usual picture, and the reaction can be delayed by hours, which makes a written diary more reliable than memory.

How to spot it on a label

Scan the ingredients list for any of these:

• E133
• Brilliant Blue or Brilliant Blue FCF
• Blue 1 or FD&C Blue 1

A practical tip: whenever a product is green, assume the colour may be a blue-plus-yellow blend and read the full colour line. Checking green products, not just blue ones, is the step people most often miss.

A balanced take on the evidence

It is worth staying proportionate. Brilliant Blue is one of the better-tolerated synthetic colours, it is not an azo dye, and it does not carry the children’s behaviour warning. Health authorities regard it as safe within the permitted limits, and the skin reports, while real, are relatively rare and tend to cluster in people who already react to multiple additives.

So there is no need to treat Brilliant Blue as a serious hazard if you have no history of colour-related skin trouble. If you do have unexplained hives, it belongs on the list of things to consider, but usually as a minor player rather than the main event, and often alongside the yellow it is blended with in green products.

What to do if you suspect it triggers your skin

If you think Brilliant Blue might be affecting your skin, work through it calmly:

1. Keep a symptom diary. Note brightly coloured drinks and sweets, and include non-food sources like mouthwash and medicines, with times, so a delayed reaction is not missed.
2. Check green products too. Because green is usually blue plus yellow, a reaction to a green item may point to the yellow, which could be an azo dye worth screening for separately.
3. Try uncoloured or naturally coloured swaps. Comparing a plainer version of the same product gives a cleaner test than removing whole food groups.
4. Talk to a professional. See a GP or allergist if reactions are frequent or severe, and treat rapid swelling or breathing difficulty as an emergency by calling 999. Any elimination, particularly for a child, is best done with a registered dietitian’s guidance.

This article is educational and is not medical advice. Its purpose is to help you ask better questions, not to replace a proper assessment.

Check products against your list

A free scanner like Yuka gives a packaged product a general health score, a useful broad read, though that verdict is the same for everyone rather than tuned to your skin. Fig is genuinely good if you are managing a defined eating pattern. To check a product against the specific things that make your skin react, a personal-list app like ClearaScan lets you save your triggers once and scan any product, food, medication or cosmetic, against your ingredient guard list, flagging only yours. So if Brilliant Blue (E133) is on your list, it flags a blue or green sweet, drink or mouthwash that contains it while ignoring everything that does not concern you. 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.)

Written and reviewed by the Sensitive Skin Lab editorial team.