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Moumoujus

HC BLUE NO. 2.

Questionable CAS 33229-34-4 / HAIR DYEING

HC Blue No. 2 is an aromatic amine, primarily utilized as a non-oxidative, direct blue hair dye. Its small molecular structure allows it to penetrate hair fibers, imparting color without requiring oxidative reactions. While widely used in hair products, its application in skincare formulations would solely be for cosmetic coloring.

Summary

Cosmetic Colorant

Science

Mechanism of Action

As a direct colorant, HC Blue No. 2's mechanism involves the diffusion of its low molecular weight particles into the hair shaft, where it deposits color. For skin, its interaction is limited to surface staining or acting as a cosmetic pigment within a formulation; no active physiological or therapeutic mechanism on skin is established by current research.

Research

Clinical Evidence

Insufficient-data confidence
Effective range N/A
Optimal

N/A

Transparency

Dusting Analysis

Not commonly dusted

No specific data is available regarding dusting concerns or thresholds for HC Blue No. 2. Standard handling practices for fine powders are advisable.

The Formula

Formulation

Solubility
Both
Optimal pH ≤9
0 7 14

Stability

This colorant exhibits stability under typical storage conditions, though protection from light, heat, and dust is recommended. Optimal color retention in formulations occurs in alkaline environments, but pH levels should not exceed 9.0 to prevent decomposition. It is prone to nitrosation due to its amino groups and requires storage under an inert gas atmosphere for extended stability in solutions.

Conflicts

  • Anionic surfactants or detergents (due to its positive charge)
  • Salts or electrolytes (may impact color longevity)
  • Oxidizing agents
  • Nitric acid
  • Chlorates

Safety

Safety Profile

CIR Status
Safe as used
Max tested
2.8%
Sensitization risk Moderate

The Cosmetic Ingredient Review (CIR) Expert Panel and the EU's Scientific Committee on Consumer Products (SCCP) both concluded HC Blue No. 2 is safe for use in hair dye products at concentrations up to 2.8%. Human volunteer studies indicated minimal dermal absorption (less than 0.1% over 30 days) and no sensitization at typical use concentrations. However, aggregated GHS classifications for the raw material suggest a potential for allergic skin reactions (H317 in 40.5% of reports) and some equivocal data regarding skin sensitizing potential in mice, leading to a moderate sensitization risk consideration.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Questionable

Primarily utilized as a direct blue hair dye, HC Blue No. 2 shows no established benefits for skin health and presents a moderate risk of skin irritation or sensitization, making its inclusion in precision skincare formulations questionable.

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