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Moumoujus

OXALIC ACID.

Questionable CAS 144-62-7 / CHELATING

Oxalic acid acts as a chelating agent and, in higher concentrations, as an Alpha Hydroxy Acid (AHA) to promote skin exfoliation. Despite its exfoliating potential, this ingredient carries significant safety concerns, including corrosivity and potential for tissue damage.

Summary

chelating exfoliating

Science

Mechanism of Action

This dicarboxylic acid primarily functions as a chelating agent, binding to metal ions, which can influence cosmetic product stability and appearance. As an AHA, particularly in elevated concentrations and an acidic pH range (e.g., pH 3-4), it can facilitate the desquamation of dead skin cells from the stratum corneum, thereby potentially improving skin texture and elasticity, especially for oily skin types. However, oxalic acid is also noted to irritate tissues, induce inflammation, damage skin cells, compromise the skin barrier, and degrade structural components like collagen and hyaluronic acid, largely due to its ability to immobilize calcium.

Research

Clinical Evidence

Insufficient-data confidence
Effective range N/A
Optimal

N/A

Transparency

Dusting Analysis

Not commonly dusted

The Formula

Formulation

Solubility
Water
Optimal pH 3 – 5.5
0 7 14

Stability

Oxalic acid exhibits pKa values around 1.25-1.46 and 4.28-4.40. For AHA-driven exfoliation, optimal efficacy is observed between pH 3.2-3.9, with general effectiveness within pH 3-4. Overall, stability is considered optimal below pH 5.5, with instability noted in neutral-to-alkaline formulations.

Conflicts

  • Metal ions (due to chelating properties, which can destabilize formulations and alter appearance)
  • Other strong active ingredients (e.g., multiple exfoliating acids, retinoids, benzoyl peroxide) due to increased risk of irritation, dryness, and skin barrier disruption
  • Vitamin C (ascorbic acid) due to potential pH destabilization

Safety

Safety Profile

CIR Status
Not reviewed
Max tested
5%
Sensitization risk High

In the European Union, oxalic acid is restricted to a maximum concentration of 5% in cosmetic products, as per Annex III of the EC Cosmetics Regulation following an SCCS assessment. While the Cosmetic Ingredient Review (CIR) has not specifically assessed oxalic acid, it has reviewed other AHAs generally. In the U.S., the FDA does not require pre-market approval for cosmetic ingredients, and oxalic acid is not explicitly prohibited. However, the EPA has classified oxalic acid in Toxicity Category I for acute eye and skin irritation, indicating its corrosive nature. It can harm skin by causing irritation, inflammation, cellular damage, weakening the skin barrier, and degrading collagen and hyaluronic acid.

Your Skin

Skin Compatibility

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

Our Assessment

Verdict

Questionable

While oxalic acid exhibits chelating and exfoliating properties, its classification as a Toxicity Category I irritant and corrosive agent, alongside its potential to damage skin components, warrants extreme caution and questions its suitability for precision skincare formulations.

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