European Commission Confirms Safety of HC Yellow No. 16 Hair Dye Ingredient

Background

The SCCS, an independent body providing scientific advice to the European Commission, evaluates the safety of non-food consumer products, including cosmetics. The committee's recent assessment focused on HC Yellow No. 16, a colourant widely used in hair dye formulations due to its vibrant yellow hue and stability in various chemical environments.

The ingredient first came under review in 2015 when the European Commission received a dossier from the cosmetics industry seeking approval for HC Yellow No. 16 in hair dyes. The initial SCCS opinion, issued later that year, conditionally approved its use, highlighting concerns about the purity and impurity profiles of the batches tested. The committee requested further data to ensure that the ingredient met stringent safety standards, particularly regarding impurity levels and their potential health impacts.

In February 2024, the industry submitted additional data addressing these concerns, prompting the SCCS to re-evaluate the ingredient's safety based on new commercial batches produced with improved manufacturing processes.

Key Findings

1. Safety in Formulations:
   • The SCCS concludes that HC Yellow No. 16 is safe when used as an ingredient at concentrations of 1% in oxidative hair dye formulations and 1.5% in non-oxidative hair dye formulations.
   • This conclusion is based on the improved purity and reduced impurity levels in the new commercial batches compared to those previously assessed. The committee emphasised that adherence to these concentration limits is crucial for ensuring consumer safety.
2. Purity and Impurities:
   • The updated data show that the purity of HC Yellow No. 16 has been significantly enhanced, with overall purity levels exceeding 99%.
   • The levels of heavy metals (arsenic, lead, cadmium, mercury, and iron) in the new batches were found to be below quantifiable limits, indicating that the ingredient meets the strict safety standards required for cosmetic use.
   • Three specific impurities were identified in the new batches, but their concentrations are within safe limits as per the Threshold of Toxicological Concern (TTC) approach. These impurities include 2-chloro-6-((1-methyl-1H-pyrazol-5-yl)diazenyl)phenol, 2-chloro-4,6-bis((E)-(1-methyl-1H-pyrazol-5-yl)diazenyl)phenol, and an unnamed compound with similar chemical properties.
3. Chemical and Physical Specifications:
   • HC Yellow No. 16 is characterised as a yellow powder with a molecular weight of 236.7 g/mol. It has limited solubility in water but demonstrates good solubility in various organic solvents, such as methanol and dimethyl sulfoxide (DMSO).
   • The ingredient's stability in oxidative conditions, which are common in hair dye formulations, was rigorously tested. Results showed that HC Yellow No. 16 remains stable without significant degradation over extended periods, ensuring its effectiveness and safety during use.
4. Toxicological Evaluation:
   • The toxicological assessment of HC Yellow No. 16, including potential impurities, was conducted using advanced methodologies. The SCCS utilised the TTC approach to evaluate the safety of impurities at low concentrations. This method is recognised for its robustness in assessing substances with limited toxicological data by comparing them to well-established safety thresholds.

Detailed Assessment

Impurity Profiles

The impurity analysis of the new batches of HC Yellow No. 16 showed significant improvements. The main impurity levels detected were:

• Impurity 5B: 2-chloro-6-((1-methyl-1H-pyrazol-5-yl)diazenyl)phenol
• Impurity 7B: 2-chloro-4,6-bis((E)-(1-methyl-1H-pyrazol-5-yl)diazenyl)phenol
• Impurity 8B: Unnamed compound with similar azo characteristics

The concentrations of these impurities were found to be well below the levels of concern, with systemic exposure doses (SED) calculated at a maximum of 0.09 µg/person/day under non-oxidative conditions and 0.04 µg/person/day under oxidative conditions. These values are substantially lower than the TTC threshold of 90 µg/person/day, confirming their safety.

Stability and Reactivity

The stability of HC Yellow No. 16 in the presence of alkaline peroxide was evaluated to simulate typical conditions in oxidative hair dye applications. The results indicated that HC Yellow No. 16 maintains its integrity and does not degrade into harmful by-products over a standard application period. This stability is crucial for ensuring consistent performance and safety in cosmetic products.

Conclusion

The SCCS’s latest scientific advice reinforces the safe use of HC Yellow No. 16 in hair dye products, provided that manufacturers adhere to the specified concentration limits. This decision provides reassurance to both consumers and manufacturers regarding the continued use of this ingredient in cosmetic formulations.

The committee's rigorous assessment process, which included comprehensive chemical and toxicological evaluations, underscores the European Commission's commitment to consumer safety and public health. By ensuring that cosmetic ingredients meet high safety standards, the SCCS helps protect consumers from potential risks associated with cosmetic products.

About the SCCS

The SCCS is part of the European Commission's efforts to ensure consumer safety, public health, and environmental protection. The committee comprises independent scientific experts who provide opinions on the safety of non-food consumer products. These opinions inform regulatory policies and ensure that products on the market are safe for consumers.

In addition to the SCCS, the European Commission relies on the expertise of other scientific bodies, such as the European Food Safety Authority (EFSA), the European Medicines Agency (EMA), and the European Chemicals Agency (ECHA), to safeguard public health and safety.