Caprylhydroxamic Acid (CHA) – Preservative Booster / Articles

Caprylhydroxamic Acid (CHA): Properties and Applications

1. Introduction

Caprylhydroxamic acid (CHA), also known as octanohydroxamic acid, is a multifunctional cosmetic ingredient belonging to the hydroxamic acid class. It is valued as a gentle preservative booster and chelating agent that enhances the efficacy of preservation systems while maintaining formulation mildness. CHA is increasingly used in cosmetics and personal care products as an alternative to parabens and other harsh preservatives, particularly in clean beauty and natural formulations.

2. Chemical Structure and Properties

Chemical name: Octanohydroxamic acid; N‑Hydroxyoctanamide

Molecular formula: C₈H₁₇NO₂

Molecular weight: 159.23 g/mol

CAS number: 7377-03-9

Appearance: White to off‑white crystalline powder

Solubility: Limited in water (approx. 1.55 g/L); soluble in alcohols, glycols (propylene glycol, glycerin), phenoxyethanol, and surfactants

pH range: Effective up to pH 7.5

Recommended usage: 0.05–0.25% in formulations

3. Mechanism of Action

Chelation: The hydroxamic acid functional group makes CHA an excellent chelating agent. It forms strong complexes with transition metal ions, particularly iron (Fe³⁺). By sequestering metals essential for microbial metabolism, CHA creates an environment that inhibits microbial growth.

Antimicrobial activity: CHA demonstrates strong efficacy against a broad spectrum of microorganisms, especially yeasts and molds. Unlike most organic acids used in preservation, CHA remains undissociated at neutral pH, allowing it to function effectively across a broad pH range up to 7.5.

Preservative synergy: When combined with glycols (such as caprylyl glycol, pentylene glycol, or propanediol) and phenoxyethanol, CHA provides synergistic antimicrobial protection, enabling lower concentrations of traditional preservatives.

4. Applications

Skin care: Creams, lotions, serums, and moisturizers – provides preservation and metal chelation, preventing oxidative degradation and microbial contamination.

Hair care: Shampoos, conditioners, and hair masks – extends shelf life while remaining gentle on the scalp.

Color cosmetics: Foundations, BB creams, and lip products – stabilizes formulations by chelating metal ions.

Natural and clean beauty: Particularly valued in preservative‑free and natural formulations as an alternative to parabens, formaldehyde donors, and other harsh preservatives.

Pharmaceuticals: Used in manufacturing due to its chelating abilities.

5. Safety and Toxicology

Regulatory status: The Cosmetic Ingredient Review (CIR) Expert Panel has concluded that caprylhydroxamic acid is safe in cosmetics at current practices of use and concentrations. It is listed in the European CosIng database as an approved cosmetic ingredient.

Skin irritation: CHA is considered a gentle preservative with low irritation potential. However, emerging evidence suggests it may be a contact allergen in some cases, particularly on damaged skin.

Environmental profile: 100% natural, biodegradable, and derived from vegetable sources (coconut oil). Readily biodegradable (98% after one month).

6. Formulation Guidelines

Recommended use levels: 0.05–0.25% of the formulation.

Solubilization: Dissolve in glycols (propylene glycol, glycerin), phenoxyethanol, or surfactants before adding to the water phase.

Processing: Avoid prolonged heating above 60°C (max 6 hours) or 90°C (max 2 hours).

Compatibility: Compatible with most cosmetic ingredients. Works synergistically with phenoxyethanol, glycols, ethylhexylglycerin, and other mild preservatives.

7. Advantages and Limitations

Advantages:

Multifunctional – combines chelating, antimicrobial, and preservative‑boosting properties.
Effective at low concentrations (0.05–0.25%).
Works at neutral pH (up to 7.5) – unlike many organic acids.
Natural, biodegradable, and derived from renewable sources.
Reduces dependence on parabens and other harsh preservatives.
Gentle on skin with low irritation potential.

Limitations:

Limited water solubility requires pre‑dissolution in glycols or surfactants.
May be less effective against bacteria; best used in combination with bacteria‑specific preservatives.
Emerging allergen; patch testing recommended for leave‑on products.

8. Conclusion

Caprylhydroxamic acid (CHA, CAS 7377-03-9) is a multifunctional chelating agent and preservative booster that offers effective antimicrobial protection, particularly against yeasts and molds, while maintaining formulation mildness. Its ability to function at neutral pH, combined with natural origin and biodegradability, makes it a valuable ingredient for modern cosmetic formulations, especially in clean beauty and natural product segments. When used in combination with glycols and other mild preservatives, CHA provides robust preservation with a favorable safety profile.