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be sonatural, Face masks, read from the back

CI 42090

Blue 1

Well toleratedColourantcolourant

No meaningful concern for most people; irritation is possible but rare.

Also written as: Blue 1 · Acid Blue 9 · FD&C Blue No. 1 · Brilliant Blue FCF · E 133

What it is

CI 42090 is a water-soluble triphenylmethane dye, the same substance approved as the food colour E 133. In cosmetics it provides the vivid blue of aqua gel masks and blue clay products, usually at very low levels. Unlike iron oxides it dissolves rather than sitting on the surface as a pigment.

What it does well

  • Delivers a strong blue at very low use levels

    Its intensity means only trace amounts are needed, which keeps total exposure low. This is a purely aesthetic function.

    Strong evidence

Worth knowing

  • Occasional contact allergy

    Synthetic dyes are a more plausible source of contact allergy than mineral pigments, though reported cases with CI 42090 are uncommon. It was reviewed by the EU's cosmetics scientific committee in 2004 as Acid Blue 9.

    Matters most toPeople with a history of reacting to coloured cosmetics or to azo and triarylmethane dyes.

Where the EU stands

Concentration-restricted

Permitted as a cosmetic colourant with no concentration limit, subject to the E 133 purity criteria. A separate restriction applies to its use as a hair dye, where it is capped at 0.5% in non-oxidative hair dye products.

Regulation (EC) No 1223/2009, Annex IV entry 63 (colourant); Annex III entry 190 (Acid Blue 9 as a hair dye substance) · source ↗

Masks that contain CI 42090