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Hair Dye Precursor

1H-Indole-5,6-diol

CAS 3131-52-0
25

Safety score · 0–100

Caution

Derived from EU CosIng regulatory status, PubChem hazard data and published research. How we score.

5,6-Dihydroxyindole is a melanin precursor used in oxidative hair dye systems. Multiple GHS hazards including serious eye damage and aquatic toxicity, plus SCCS sensitisation concerns, place it in the red tier.

Function

HAIR DYEING

Skin benefits

  • Precursor in melanin synthesis, used in some hair dye chemistries
  • Can give natural-looking dark shades

Known concerns

  • PubChem GHS: H302 harmful if swallowed, H318 serious eye damage, H411 toxic to aquatic life
  • Strongly reactive catechol-amine motif with oxidation risk
  • SCCS has flagged dihydroxyindole hair dye precursors for sensitisation and genotoxicity assessment
  • Possible skin staining and contact dermatitis
  • Not approved for general leave-on cosmetic use

References

EU

EU CosIng database

European Commission cosmetic ingredient registry: regulatory status, restrictions, authorised functions.

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This profile is for educational purposes and does not constitute medical advice. Regulatory status and scientific understanding evolve, so always read the physical product label and consult a healthcare professional for personal concerns.