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4-NITRO-O-PHENYLENEDIAMINE.

Avoid CAS 99-56-9 / HAIR DYEING

A substituted aromatic amine compound primarily utilized as a colorant in hair dye formulations. This ingredient functions as both a direct dye penetrating hair shafts and as a precursor molecule in oxidative systems where it forms complex pigment structures.

hair dyeing

Science

Penetrates hair fibers due to its small molecular size, either depositing color directly in semi-permanent applications or undergoing chemical reactions within the hair shaft to create larger pigment molecules in permanent dye systems.


Research

High confidence
Effective range 0.049–0.5%
Optimal

0.5%

Key findings

  1. 01 SCCP safety evaluation at 0.5% concentration with margin of safety calculated at 357
  2. 02 Human repeat insult patch testing on 206 volunteers at 0.049% showing no adverse reactions
  3. 03 Guinea pig sensitization studies at 3.0% demonstrating strong sensitization potential

Transparency

Not commonly dusted

This ingredient is exclusively used in hair coloring applications and not incorporated into skincare formulations, making dusting analysis irrelevant.


The Formula

Solubility
Water
Optimal pH 9 – 10.5
0 7 14

Stability

Requires alkaline environment for stability and efficacy, sensitive to oxidation and requires protection from light and air exposure

Conflicts

  • Strong oxidizing agents
  • Strong acids
  • Iron and copper salts

Safety

CIR Status
Safe with restrictions
Max tested
0.5%
Sensitization risk High

Approved for hair dye use only when formulated to minimize sensitization risk. European regulations restrict to maximum 0.5% in finished products applied to scalp.


Your Skin

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

Our Assessment

Avoid

This ingredient is designed exclusively for hair coloring applications and should not be used in facial or body skincare products.


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