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BASIC RED 51.

Optional CAS 77061-58-6 / HAIR DYEING

A high-intensity cationic azo dye primarily used for temporary and semi-permanent color deposition. It adheres to surfaces through electrostatic attraction, providing vibrant red hues without requiring deep chemical penetration.

colorant hair dye

Science

As a positively charged (cationic) molecule, it binds to the negatively charged carboxyl groups found in hair and skin proteins. It remains on the surface rather than entering the cortex, though in cellular environments, it has been observed to trigger oxidative stress and influence cell cycle regulation.


Research

Medium confidence
Effective range 0.5–1%
Optimal

1%

Key findings

  1. 01 Established as the maximum safe threshold for non-oxidative applications by the SCCS.
  2. 02 Identified as a cytotoxic threshold in human keratinocytes, potentially inducing DNA damage.

Transparency

Not commonly dusted
Min. effective
0.1%
Red flag below
0.05%

In color-depositing products, concentrations below 0.1% typically fail to provide visible aesthetic results, making lower amounts purely 'label dressing'.


The Formula

Solubility
Water
Optimal pH 3.5 – 9
0 7 14

Stability

Maintains peak stability between pH 4.0 and 7.0; however, it is prone to degradation under intense UV light or temperatures exceeding 200°C.

Synergies

  • Non-ionic surfactants
  • Cationic conditioning agents

Conflicts

  • Anionic surfactants
  • Strong electrolytes
  • Strong oxidizing agents

Safety

CIR Status
Not reviewed
Max tested
1%
Sensitization risk Low

While safe for topical rinse-off use, in-vitro data suggests potential genotoxic risks if absorbed, leading to strict regulatory limits in the EU.


Your Skin

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

Our Assessment

Optional

An effective temporary colorant with a narrow safety margin and specific formulation requirements that limit its use to rinse-off hair care.


Related

Finding similar ingredients…


References