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P-PHENYLENEDIAMINE SULFATE.

Avoid CAS 16245-77-5 / HAIR DYEING

P-Phenylenediamine Sulfate is an essential precursor utilized in permanent oxidative hair coloring systems. It chemically reacts within the hair shaft to form stable, colored molecules, providing long-lasting hair color. However, its high reactivity and known sensitizing properties necessitate careful application and restrict its use in direct dermal applications.

Summary

Hair Dyeing Hair Colorant

Science

Mechanism of Action

P-Phenylenediamine Sulfate acts as a primary intermediate in permanent hair dyeing. When combined with an oxidizing agent like hydrogen peroxide, it undergoes an oxidative polymerization reaction inside the hair shaft. This process generates larger, colored compounds that become entrapped, imparting a durable color change. Importantly, surface oxidation of P-Phenylenediamine on the skin can also trigger allergic sensitization reactions.

Research

Clinical Evidence

High confidence
Effective range 2–6%
Optimal

N/A

Key findings

  1. 01 Permitted concentration for hair dyeing in the EU is 2% (calculated as free base) when mixed with hydrogen peroxide.
  2. 02 Reported concentrations for P-Phenylenediamine Sulfate in hair dye formulations typically reach 6%.

Transparency

Dusting Analysis

Not commonly dusted

P-Phenylenediamine Sulfate functions as a primary ingredient for permanent hair coloration, not a skincare active intended for dermal benefits. Therefore, the concept of 'dusting' related to insufficient active concentration for skin efficacy is not applicable to its intended use.

The Formula

Formulation

Solubility
Water
Optimal pH N/A
0 7 14

Stability

This ingredient is prone to oxidation upon exposure to air or other oxidizing materials, leading to discoloration (purple or black). Its reactivity and the resulting color formation in hair dyes are significantly influenced by the solution's pH, with the pKa of its base form being 6.31.

Synergies

  • Hydrogen peroxide (for the intended oxidative hair dyeing reaction)

Conflicts

  • Strong oxidizing agents (when not part of the intended dyeing system)
  • Atmospheric oxygen (leading to premature oxidation and discoloration)
  • Individuals with a history of sensitization to P-Phenylenediamine or related compounds

Safety

Safety Profile

CIR Status
Safe with restrictions
Max tested
6%
Sensitization risk High

The CIR Expert Panel considers P-Phenylenediamine Sulfate safe for use in hair dye products for non-sensitized individuals at current concentrations. However, it is explicitly deemed unsafe for direct dermal coloring applications (e.g., black henna tattoos) and for use in eyelash and eyebrow dyes due to its significant sensitizing potential. The EU Cosmetics Directive (SCCS) lists it in Annex III, permitting its use as an oxidizing hair colorant up to 6% (calculated as free base), translating to a maximum of 2% PPD on the head after mixing. Consumers are advised to follow label instructions, especially patch testing, to identify and prevent exposure if sensitized. This ingredient's safety assessment was reaffirmed in 2007 and is presently under a draft amended review as of November 2023.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Avoid

As a potent hair dye ingredient with a high risk of sensitization and irritancy, P-Phenylenediamine Sulfate is explicitly unsuitable for direct use in precision skincare formulations.

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