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4-AMINO-2-HYDROXYTOLUENE.

Avoid CAS 2835-95-2 / HAIR DYEING

4-amino-2-hydroxytoluene is a synthetic aromatic compound that functions as a color coupler in oxidative hair dye formulations. While deemed safe for its intended hair coloring applications at concentrations up to 1.5%, this ingredient poses sensitization risks and has no established role in skincare products.

hair dyeing

Science

Functions as a secondary intermediate that reacts with primary dye precursors in the presence of hydrogen peroxide to form larger, stable color molecules within the hair shaft structure.


Research

High confidence
Effective range 1–1.5%
Optimal

1.5%

Key findings

  1. 01 SCCS patch testing at 1.5% demonstrated sensitization potential, particularly in individuals pre-sensitized to p-phenylenediamine
  2. 02 CIR evaluation at 1.0% confirmed effective color coupling in oxidative hair dye systems

Transparency

Not commonly dusted

Not applicable for skincare formulations as this ingredient is exclusively designed for hair coloring applications


The Formula

Solubility
Water
Optimal pH 9 – 10.5
0 7 14

Stability

Requires oxygen-free storage conditions and alkaline pH environment; degrades rapidly upon air exposure

Synergies

  • p-phenylenediamine (primary intermediate)
  • hydrogen peroxide (oxidizing agent)

Conflicts

  • Strong oxidizing agents
  • Strong acids
  • Air/oxygen exposure

Safety

CIR Status
Safe as used
Max tested
1.5%
Sensitization risk High

Classified as a skin sensitizer with particular concern for individuals already sensitized to related aromatic amines


Your Skin

No Normal
No Dry
No Oily
No Sensitive
Irritancy Low
Comedogenicity Unknown

Our Assessment

Avoid

Exclusively a hair dye ingredient with sensitization risks and no skincare benefits.


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