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SODIUM METASILICATE.

Questionable CAS 6834-92-0 / ANTICORROSIVE, BUFFERING, CHELATING

Sodium Metasilicate is a highly alkaline inorganic salt utilized in cosmetic formulations primarily as a corrosion inhibitor and chelating agent. Its strong alkalinity necessitates precise formulation to ensure skin compatibility and prevent irritation.

Summary

Corrosion inhibitor Chelating agent pH adjuster Emulsifying agent Dispersing agent

Science

Mechanism of Action

This inorganic salt exerts its effects by buffering pH to a strongly alkaline range, typically between 12.4 and 12.7, in aqueous solutions. It functions as a corrosion inhibitor, protecting metal components, and a chelating agent, effectively binding metal ions. Additionally, it offers purifying, emulsifying, and dispersing properties, which are leveraged in various cosmetic and cleaning applications.

Research

Clinical Evidence

Low confidence
Effective range N/A
Optimal

N/A

Key findings

  1. 01 Clinical testing revealed that Sodium Metasilicate at a 37% concentration within a detergent, when mixed with water, acted as a severe skin irritant on both intact and abraded human skin.
  2. 02 In mouse studies, while negative in the local lymph node assay (LLNA) at up to 6%, a delayed-type hypersensitivity response was observed when mice were sensitized at 4% and subsequently challenged at 6%.

Transparency

Dusting Analysis

Not commonly dusted

The Formula

Formulation

Solubility
Water
Optimal pH 12.4 – 12.7
0 7 14

Stability

Sodium Metasilicate is a highly alkaline substance, with its solutions typically exhibiting a pH range of 12.4 to 12.7. It is a hygroscopic and deliquescent solid, meaning it readily absorbs moisture from the air and may dissolve. Hydrolysis occurs when exposed to hot water.

Conflicts

  • Acids
  • Strong oxidizers
  • Halogens (reacts violently)
  • Heat sources
  • Water/moisture (can react, potentially releasing flammable gases with certain metals)
  • Alkali-sensitive metals or alloys (e.g., aluminum, brass, bronze, copper, lead, tin, zinc)

Safety

Safety Profile

CIR Status
Safe with restrictions
Sensitization risk Moderate

The Cosmetic Ingredient Review (CIR) Expert Panel has concluded that Sodium Metasilicate is safe for use in cosmetic products provided it is formulated to prevent irritation. While reported in cosmetic formulations at concentrations between 13% and 18%, a 37% concentration was found to be a severe skin irritant. It is also designated as Generally Recognized As Safe (GRAS) by the FDA for direct food substances.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Questionable

Sodium Metasilicate is a highly alkaline ingredient demanding precise formulation to mitigate its significant potential for skin irritation and sensitization, limiting its use to specific cosmetic functions like pH adjustment and chelating.

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