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, who reacts, and where it hides.

What it is

Brilliant Blue is a synthetic blue colour, known as Brilliant Blue FCF, E133, or in the United States as FD&C Blue 1. A small accuracy point worth making: it is not an azo dye, it belongs to a different chemical family (the triarylmethane dyes). That matters because much of the worry about food colours focuses on azo dyes specifically, and Brilliant Blue is often a lower-concern option, though it is still a synthetic colour many sensitive shoppers prefer to avoid. It is frequently blended with a yellow dye to make green.

Who reacts, and how it shows on the skin

Reactions to Brilliant Blue appear to be less common than to the azo colours, but they are reported: 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 it is one of several that contribute.

Where it hides

Blue and green sweets, ice pops and slushies, sports and energy drinks, blue curacao-style mixers, some tinned processed peas, icing and cake decorations, and non-food items like mouthwash and some medicines. Look for Brilliant Blue, E133 or Blue 1, and remember that a green product often contains both this and a yellow colour.

What to do if you think you react

Keep a food-and-skin diary and note brightly coloured drinks and sweets in particular. If you react, check green products too, since the green is usually a blue-plus-yellow blend and the yellow may be an azo dye you also want to screen for. See a GP or allergist if reactions are frequent or severe.

Check it against your own 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. 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.)