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HYDROXYPROPYL-P-PHENYLENEDIAMINE.

Avoid CAS 73793-79-0 / HAIR DYEING

Hydroxypropyl-p-phenylenediamine is primarily an oxidative hair dye precursor, reacting with an oxidizing agent to impart permanent color to hair. While deemed safe for this specific use at concentrations up to 2% by the SCCS, it presents a moderate potential for skin sensitization and mild to moderate eye irritation.

Summary

Hair Dyeing

Science

Mechanism of Action

This compound functions by participating in chemical reactions with oxidizing agents, like hydrogen peroxide, to create colored molecules that become fixed to the hair structure. While primarily active on hair, a minor fraction may permeate the scalp, where the body typically detoxifies it. However, any portion not detoxified can undergo auto-oxidation, generating derivatives that might bind to skin proteins, thereby posing a risk for sensitization.

Research

Clinical Evidence

High confidence
Effective range ≤2%
Optimal

N/A

Key findings

  1. 01 The SCCS Final Opinion (SCCS/1659/23) established its safety for use in oxidative hair coloring at a maximum on-head concentration of 2%.
  2. 02 Animal data indicates a moderate skin sensitizer potential and mild to moderate eye irritation at 2%.
  3. 03 An in-vitro EpiskinSM skin irritation test at 2% suggested non-irritating potential for skin, while a bovine corneal test at 2% suggested slight ocular irritancy.

Transparency

Dusting Analysis

Not commonly dusted

This ingredient's primary function is as a hair dye precursor, not a skincare active, rendering the concept of 'dusting' inapplicable to its use in skincare formulations.

The Formula

Formulation

Solubility
Water
Optimal pH N/A
0 7 14

Stability

The dihydrochloride salt of this compound is water-soluble. Protection from air and oxidation is critical, as related p-phenylenediamine oxidizes to form undesired colors upon air exposure, leading to formulation instability.

Conflicts

  • Oxidizing materials (beyond the controlled reaction with hydrogen peroxide for hair dyeing)
  • Air (promotes auto-oxidation and color alteration)
  • Caustic soda (based on data for related compounds)

Safety

Safety Profile

CIR Status
Not reviewed
Max tested
2%
Sensitization risk Moderate

The Scientific Committee on Consumer Safety (SCCS) has affirmed its safety for oxidative hair coloring at a maximum on-head concentration of 2%, having addressed prior genotoxicity concerns. However, animal data indicates a mild to moderate eye irritation potential and a moderate potential for skin sensitization. It is not approved for general cosmetic use under EU regulations, only for hair dyeing applications.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Avoid

Primarily functioning as an oxidative hair dye precursor, this ingredient is not recommended for precision skincare formulations due to its moderate skin sensitization potential and mild to moderate eye irritation risk.

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