Get a Free 5ml Mini Now Free 5ml Mini With Every Order of The Mantle
Moumoujus

N-PHENYL-P-PHENYLENEDIAMINE.

Avoid CAS 101-54-2 / HAIR DYEING

N-Phenyl-p-Phenylenediamine, also known as p-Phenylenediamine (PPD), is an aromatic amine primarily utilized as an oxidative dye precursor. While essential for permanent hair coloration, its interaction with skin is associated with significant sensitization and irritation.

Summary

Oxidative Hair Colorant Dye Precursor

Science

Mechanism of Action

This compound acts as an oxidative dye precursor, reacting with oxidizing agents like hydrogen peroxide to form stable colored products that bind permanently to hair. On the skin, its oxidation products are highly reactive substances capable of interacting with tissue nucleophiles. Specifically, N-Phenyl-p-Phenylenediamine can activate mast cells via the MRGPRX2 receptor, initiating an immediate contact allergy, releasing tryptase, and potentially causing non-histaminergic itching. Allergic reactions are triggered by its oxidation on and within the skin, with metabolic activation steps potentially leading to mutagenic and carcinogenic compounds.

Research

Clinical Evidence

Low confidence
Effective range N/A
Optimal

N/A

Key findings

  1. 01 The CIR Expert Panel deemed N-Phenyl-p-Phenylenediamine safe for use in hair dyes at concentrations up to 1.7% (as free base). The European Union permits up to 4% (as free base) in hair dyes, reducing to 2% when mixed with hydrogen peroxide.
  2. 02 For diagnostic patch testing, 0.3% is recommended to confirm sensitization with a reduced risk of severe reactions, while 1% is a standard but can elicit severe blistering. A threshold of 38 ppm (0.0038%) has been identified for positive patch test reactions in 10% of tested individuals.

Transparency

Dusting Analysis

Not commonly dusted

N-Phenyl-p-Phenylenediamine is recognized for its role in hair dyeing and is not an ingredient commonly 'dusted' or misrepresented as a skincare active. Its specific applications do not align with trending skincare claims.

The Formula

Formulation

Solubility
Both
Optimal pH N/A
0 7 14

Stability

While generally stable, N-Phenyl-p-Phenylenediamine oxidizes upon exposure to air, resulting in a purple or black discoloration. It reacts readily with oxidizing agents and should be stored under an inert atmosphere. With pKa values of 2.97 and 6.31, it exists predominantly in its neutral form (approximately 83%) at pH 7, with a minor portion as the charged ammonium species.

Conflicts

  • Oxidizing agents (e.g., hydrogen peroxide, unless specifically formulated for dyeing)
  • Air (causes oxidation and discoloration)
  • Isocyanates
  • Halogenated organics
  • Peroxides
  • Phenols (acidic)
  • Epoxides
  • Anhydrides
  • Acid halides

Safety

Safety Profile

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

The CIR Expert Panel concluded N-Phenyl-p-Phenylenediamine is safe for hair dye use at up to 1.7% (as free base) but explicitly unsafe for dermal coloring applications (e.g., 'black henna' tattoos) and for eyelash/eyebrow dyes. It is a known skin irritant and potent sensitizer, with approximately 5% of the population exhibiting sensitivity, and higher incidence among hairdressers. European Union regulations prohibit its use in topical products for superficial purposes, though it is allowed in oxidative hair dyes up to 4% (free base) or 2% when mixed. Products containing it must bear warnings about potential allergic reactions and contraindicate use on eyelashes or eyebrows. The EPA has not classified its carcinogenicity.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Avoid

N-Phenyl-p-Phenylenediamine is a potent sensitizer and irritant, strictly restricted from direct skin contact or dermal applications, rendering it unsuitable for precision skincare formulations.

Related

Similar Ingredients

Finding similar ingredients…