1H-Indole-5,6-diol
Safety score · 0–100
Moderate
Derived from EU CosIng regulatory status, PubChem hazard data and published research. How we score.
About
A dihydroxyindole hair dye precursor used in oxidative hair coloring, restricted in EU formulations due to sensitization potential and limited toxicological data.
1H-Indole-5,6-diol (CAS 3131-52-0) is an intermediate in the biosynthetic pathway of eumelanin (black-brown pigment) and is used in oxidative hair dyeing formulations to achieve natural dark shades. EU Regulation 1223/2009 Annex III restricts its use to concentrations below 0.1% as a constituent of substances or mixtures. The compound lacks extensive toxicological characterization, and the dihydroxy aromatic structure raises concerns about potential for oxidative stress and quinone formation, which may contribute to sensitization.
Function
Skin benefits
- Used in oxidative hair dyeing for dark brown and black shades
- Contributes to natural-looking gray coverage
- Develops color when combined with oxidative couplers
Known concerns
- Restricted to <0.1% in EU mixtures
- Limited toxicological data available
- Potential for oxidative stress and quinone formation
- Sensitization concern from dihydroxy aromatic structure
References
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 — always read the physical product label and consult a healthcare professional for personal concerns.