Science
Mechanism of Action
As a direct hair dye, HC Blue No. 15 imparts color by adhering to the hair surface for temporary effects or diffusing into the hair shaft for semi-permanent coloration. This mechanism is specific to hair structures and does not translate into beneficial physiological actions for skin health.
Research
Clinical Evidence
Low confidenceN/A
Key findings
- 01 Studies evaluating HC Blue No. 15 primarily focus on its safety and performance as a hair dye, not its efficacy for skin. A maximum concentration of 0.2% was deemed safe by the SCCS for use in oxidative and non-oxidative hair dye formulations applied to the hair/scalp.
- 02 Direct topical application of 0.5 g (undiluted) HC Blue No. 15 to rabbit skin under semi-occlusive conditions induced mild, reversible erythema, oedema, and scaling, accompanied by marked blue staining that persisted for 14 days.
- 03 Instillation of a 2% aqueous solution (pH 6.30) into rabbit eyes caused early-onset and severe ocular irritation, leading to premature sacrifice for ethical reasons.
Transparency
Dusting Analysis
HC Blue No. 15 is predominantly used as a hair dye and does not possess known dermatological benefits that would necessitate its use or 'dusting' in precision skincare formulations.
The Formula
Formulation
Stability
The ingredient demonstrates stability within a pH range of 3.5 to 9.0, with decomposition occurring if the pH exceeds 9.0. It remains stable in solutions of DMSO and acetone at room temperature for at least 8 days. However, in buffered water solutions at pH 7.6, approximately 50% loss in concentration was observed over 8 days. Notably, it showed stability for at least 10 months in a common market formulation. It is soluble in methanol, partially soluble in water (e.g., 3.0% at pH 2.9), and soluble in various organic solvents including toluene, methylene chloride, benzene, and DMSO.
Conflicts
- Anionic surfactants or detergents, due to its positive charge.
- Salts or electrolytes, which can diminish color longevity in formulations.
Safety
Safety Profile
The Scientific Committee on Consumer Safety (SCCS) considered HC Blue No. 15 safe for consumers when used as a direct dye in hair dye formulations at a maximum concentration of 0.2% on the scalp, in both oxidative and non-oxidative applications. However, external safety assessments, such as EWG, classify HC Blue No. 15 as 'Unacceptable' for EWG VERIFIED products. Clinical studies demonstrated mild, reversible skin irritation (erythema, oedema, scaling) and significant, persistent blue staining on rabbit skin with undiluted application. Severe ocular irritation, necessitating premature sacrifice, was observed in rabbit eye instillation at a 2% aqueous solution. The outcome of the local lymph node assay for sensitization in mice was not provided.
Your Skin
Skin Compatibility
Our Assessment
Verdict
HC Blue No. 15 is a hair colorant with no known benefits for skin and presents significant irritation risks, particularly to the eyes, making it unsuitable for precision skincare formulations.
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