Ingredient

4-Amino-2-Hydroxytoluene

High risk

Also known as5-amino-o-cresol, 2-hydroxy-4-aminotoluene, 4-amino-2-hydroxytoluene, CAS 2835-95-2

FunctionDye coupler — common allergen

What it is — 4-Amino-2-Hydroxytoluene (5-amino-o-cresol, CAS 2835-95-2) is a small synthetic aromatic amine used in permanent (oxidative) hair colour. It is a coupler: on its own it produces little colour, but when a developer is present it reacts with a primary intermediate such as p-phenylenediamine (PPD) or toluene-2,5-diamine (PTD) inside the hair shaft to form the final pigment.

What it does — Couplers decide the shade. This one contributes red, violet and warm-brown notes and is used to keep brown and dark-brown formulas from looking flat or ashy. It works alongside other couplers such as resorcinol, m-aminophenol and 2,4-diaminophenoxyethanol HCl.

Typical use — Permanent hair dyes, colour lotions and colour-depositing hair dye shampoos, normally at a fraction of a percent. In the GDS Hair Dye Shampoo it is declared in the Brown and Dark Brown formulas, together with toluene-2,5-diamine sulfate (PTD), resorcinol, m-aminophenol, p-aminophenol and 2,4-diaminophenoxyethanol HCl; it is not declared in the Black formula.

What the regulators say — It is listed in Annex III of the EU Cosmetics Regulation as a restricted hair colourant, permitted only in oxidative hair dye products with a maximum on-head concentration after mixing with developer, and the label must carry the standard hair-dye warnings ("can cause an allergic reaction", not for use under 16, 48-hour skin test). The EU Scientific Committee on Consumer Safety (SCCS) has assessed it and regards it as a skin sensitiser, which is why the warnings apply.

Safety — Treat it exactly as you would PPD or PTD: do the 48-hour patch test before every use, wear the gloves, keep the product off broken or irritated skin, rinse thoroughly and stop if you notice burning, swelling or a rash. Anyone with a known hair-dye allergy should not use products that contain it. DHALIORA discloses it on every product that contains it rather than hiding it behind a "free-from" claim. This is general information, not medical advice.

Why we grade it High: High risk — an aromatic amine hair-dye coupler in the same allergy family as PPD and PTD; a skin sensitiser restricted under Annex III of the EU Cosmetics Regulation and subject to the mandatory hair-dye warnings.
Cross-reference

Found in these DHALIORA products

Found in 0 DHALIORA products

Not currently in any DHALIORA product.

How grades are set — Risk reflects our own reading of publicly available safety data, an EWG-style reading shown at the worst-case grade we've assigned this ingredient across products. It isn't a third party's proprietary score, and it isn't medical advice. Always read the packaging and patch-test where indicated.
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