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Moumoujus

2-NITRO-P-PHENYLENEDIAMINE DIHYDROCHLORIDE.

Questionable CAS 18266-52-9 / HAIR DYEING

A nitro-substituted aromatic amine compound primarily utilized as a hair colorant and dye intermediate in both permanent and semi-permanent hair coloring systems. This water-soluble salt form functions either as a direct stain for the hair shaft or as a precursor that reacts with oxidizing agents to create larger pigment molecules. While effective for hair coloring applications, it presents significant sensitization concerns and regulatory restrictions.

Summary

hair dyeing colorant dye intermediate

Science

Mechanism of Action

Functions through dual pathways depending on formulation type: directly deposits color onto hair fibers in semi-permanent systems, or undergoes oxidative coupling reactions with hydrogen peroxide in permanent systems to form larger chromophoric molecules that penetrate and remain within the hair cortex.

Research

Clinical Evidence

Medium confidence
Effective range 0.1–1.1%
Optimal

1%

Key findings

  1. 01 117-week rat study at 1.1% concentration showed no significant tumor incidence increase when applied topically twice weekly
  2. 02 Dermal absorption study demonstrated 0.83 ± 0.69 µg eq/cm² total absorbed dose at 0.2-0.29% concentration
  3. 03 Historical usage survey confirmed effective concentrations between 0.1-1% in commercial hair dye formulations

Transparency

Dusting Analysis

Not commonly dusted

Not applicable for hair coloring ingredients as they serve specific functional purposes at established concentrations

The Formula

Formulation

Solubility
Water
Optimal pH 8 – 10
0 7 14

Stability

Dihydrochloride salt form provides enhanced water solubility and stability compared to free base, but remains vulnerable to light, heat, and oxygen exposure which trigger oxidation and unwanted color development

Synergies

  • Hydrogen peroxide (oxidative coupling)
  • Other aromatic amines (color development)

Conflicts

  • Strong oxidizing agents
  • Strong bases
  • Iron (III) chloride

Safety

Safety Profile

CIR Status
Safe with restrictions
Max tested
1%
Pregnancy
Caution
Sensitization risk High

CIR concludes safety for non-sensitized individuals in hair dye applications only. Known skin sensitizer with EU ban (Annex II) but US approval for hair coloring. Requires anaerobic storage conditions.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Questionable

Effective hair colorant with significant sensitization risks and regulatory restrictions limiting its broader cosmetic application potential.

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