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N-PHENYL-P-PHENYLENEDIAMINE HCL.

Avoid CAS 2198-59-6 / 56426-15-4 / HAIR DYEING

N-PHENYL-P-PHENYLENEDIAMINE HCL is primarily an oxidative precursor employed in permanent hair dye formulations. This ingredient is a known sensitizer and is prohibited by the FDA for use in non-hair dye cosmetic applications, including skincare.

Summary

Oxidative Hair Dye Precursor

Science

Mechanism of Action

This compound acts as an oxidative hair dye precursor, reacting with hydrogen peroxide during the hair dyeing process to form large, stable color molecules within the hair shaft. On skin, it functions as a hapten, requiring metabolic activation to become immunogenic, a process that can be influenced by dermal N-acetylation.

Research

Clinical Evidence

Low confidence
Effective range N/A
Optimal

N/A

Key findings

  1. 01 The European Union Cosmetics Directive permits N-Phenyl-p-Phenylenediamine HCl (as free base) up to 6.0% for use as an oxidative coloring agent in hair dyes.
  2. 02 The CIR Expert Panel considers concentrations up to 1.7% (as free base) safe for hair dyes in non-sensitized individuals, but deems it unsafe for direct dermal coloring applications or eye area dyes.
  3. 03 The SCCS expressed no concern regarding systemic toxicity for p-Phenylenediamine used in oxidative hair dyes at on-head concentrations, up to 2.0%.

Transparency

Dusting Analysis

Not commonly dusted

N-PHENYL-P-PHENYLENEDIAMINE HCL is not an active ingredient for skincare and its use in such products is generally prohibited, rendering the concept of 'dusting' irrelevant in this context.

The Formula

Formulation

Solubility
Water
Optimal pH 7.5 – 7.5
0 7 14

Stability

This ingredient is prone to oxidation upon exposure to air, which can lead to purple or black discoloration. It is reactive with other oxidizing materials, and its oxidized quinoneimine derivatives may hydrolyze in aqueous solutions.

Conflicts

  • oxidizing materials
  • air (oxidation)

Safety

Safety Profile

CIR Status
Safe with restrictions
Max tested
1.7%
Sensitization risk High

While the CIR Expert Panel deems N-Phenyl-p-Phenylenediamine and its related salts safe for use in hair dyes up to 1.7% (as free base) for non-sensitized individuals, its application in direct dermal coloring (e.g., temporary black henna tattoos) and eyelash/eyebrow dyes is considered unsafe. The European SCCS allows concentrations up to 6.0% (as free base) in hair dyes, but mandates specific allergen warnings. Critically, the FDA explicitly prohibits its use as a color additive in any non-hair dye cosmetic products, including skincare and eye makeup, due to its unapproved status for such applications. It is a known sensitizer, with an EC3 value of 0.06% in guinea pig studies.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Avoid

Due to its potent sensitization risk and regulatory prohibition by the FDA in non-hair dye cosmetic products, N-PHENYL-P-PHENYLENEDIAMINE HCL should be avoided in all skincare formulations.

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