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2-METHOXY-P-PHENYLENEDIAMINE SULFATE.

Questionable CAS 42909-29-5 / 66671-82-7 / HAIR DYEING

2-Methoxy-p-phenylenediamine sulfate is an oxidative dye precursor primarily used in permanent hair coloring and eyelash tinting formulations. This water-soluble compound penetrates hair shafts as a colorless molecule before reacting with oxidizing agents to form trapped pigments. While designed as a gentler alternative to traditional PPD, it still carries moderate sensitization potential requiring careful formulation.

Summary

hair dyeing oxidative color precursor

Science

Mechanism of Action

Functions as a small, colorless precursor molecule that penetrates hair cuticles and outer skin layers, then undergoes oxidative coupling reactions with hydrogen peroxide to form larger, colored pigment molecules that become permanently trapped within the hair or skin structure.

Research

Clinical Evidence

High confidence
Effective range 1.8–1.8%
Optimal

1.8%

Key findings

  1. 01 SCCS assessment (2019) confirmed safety at 1.8% maximum concentration in oxidative hair and eyelash products
  2. 02 Comparative sensitization study (Schuttelaar 2018) showed 48% cross-reactivity in PPD-allergic subjects versus 84% for PPD
  3. 03 EC3 testing determined moderate sensitization threshold at 4.3% compared to PPD's 0.1%

Transparency

Dusting Analysis

Not commonly dusted

Not applicable for cosmetic skincare formulations as this ingredient is restricted to hair and eyelash coloring products only

The Formula

Formulation

Solubility
Water
Optimal pH 9 – 11
0 7 14

Stability

Extremely oxygen-sensitive requiring air-tight packaging or dual-component systems; most stable under alkaline conditions necessary for hair cuticle opening

Conflicts

  • Oxidizing agents (causes premature color development)
  • Strong acids (destabilizes compound)
  • Heavy metal ions (catalyze unwanted reactions)

Safety

Safety Profile

CIR Status
Safe with restrictions
Max tested
1.8%
Sensitization risk Moderate

SCCS-approved up to 1.8% for oxidative hair/eyelash dyes only; contraindicated on broken skin due to sensitization risk; not suitable for general skincare applications

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Questionable

Specialized hair dye ingredient with moderate sensitization risk that has no place in precision skincare formulations.

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