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HYDROXYPROPYL BIS(N-HYDROXYETHYL-P-PHENYLENEDIAMINE) HCL.

Avoid CAS 128729-28-2 / HAIR DYEING

Hydroxypropyl Bis(N-Hydroxyethyl-p-Phenylenediamine) HCl is a substituted, dimeric aromatic amine salt integral to permanent hair coloration. It acts as a color precursor that undergoes controlled oxidative reactions within the hair fiber to establish durable dye molecules.

Summary

Hair dyeing

Science

Mechanism of Action

This ingredient functions as an oxidative hair dye precursor. Upon activation by an oxidizer, typically hydrogen peroxide, it initiates a chemical cascade within the hair shaft. This reaction generates stable dye compounds that are entrapped within the hair's structure, thereby imparting lasting color.

Research

Clinical Evidence

High confidence
Effective range 0.28–1.5%
Optimal

1.5%

Key findings

  1. 01 Represents the highest maximum concentration historically reported for this ingredient in hair dyes and colors within the US, as assessed for safety by the CIR Expert Panel.
  2. 02 The maximum permissible limit established in Europe for its use as an oxidative hair dye, reflecting regulatory safety standards.
  3. 03 Determined as the maximum safe in-use concentration (applied 'on-head') after dilution with hydrogen peroxide, based on assessments by SCCNFP (predecessor to SCCS).

Transparency

Dusting Analysis

Not commonly dusted

This ingredient's primary function is as a reactive component in hair dyeing systems, not a standalone active for skin. Consequently, 'dusting' analysis related to topical skincare application thresholds is not relevant.

The Formula

Formulation

Solubility
Water
Optimal pH N/A
0 7 14

Stability

Characterized by high water solubility, indicated by a logKow of -5 at 20°C. While specific optimal pH for inherent stability is not detailed, its application in oxidative hair dye formulations often occurs within alkaline environments. Comprehensive data on its stability in finished cosmetic solutions or marketed products is limited.

Conflicts

  • Hydrogen peroxide (uncontrolled or excess beyond specified hair dye formulations)
  • Strong oxidizing agents (generally)

Safety

Safety Profile

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

The CIR Expert Panel concluded its safety for cosmetic use as an oxidative hair dye within current practice concentrations, with the highest reported US use at 0.28%. The SCCNFP (predecessor to SCCS) permitted its use in hair dye formulations up to 3.0% (pre-mixing), with an in-use concentration not exceeding 1.5% on-head. Critically, SCCNFP identified this ingredient as a sensitizer, mandating a warning label for sensitization risk. The FDA classifies it as a 'coal tar hair dye,' requiring specific caution statements, including the potential for skin irritation and an absolute prohibition from use on eyelashes or eyebrows due to the risk of permanent blindness.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Avoid

This ingredient, while functional in its role as a permanent hair dye precursor, is unsuitable for any typical skincare application due to its high sensitization potential and severe warnings against skin irritation and ophthalmic contact.

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