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Testing Eye Safety: How Agarose Diffusion Predicts Irritation in New Cosmetics

Abstract

The evaluation of ocular irritation potential is an essential component of cosmetic safety assessment, particularly for products intended for facial and periocular application. This study investigated the cytotoxic and irritant potential of five cosmetic formulations - Face Serum, Face Mist, Face Cream Light, Face Cream Rich, and Eye Cream, using the agarose diffusion cytotoxicity assay on L929 mouse fibroblast cells.

All products were tested under identical experimental conditions in accordance with the official French method for cytotoxicity determination after diffusion in agarose gel [1]. Cytotoxicity was evaluated by measuring the diameter of cell lysis following exposure and MTT staining.

All tested formulations demonstrated no detectable cytotoxicity (mean diameter = 0.0 cm). The positive control (3% sodium dodecyl sulfate, SDS) showed expected moderate cytotoxicity (2.1 cm), confirming assay validity.

Despite the presence of high levels of active ingredients, including a full spectrum of amino acids and complex formulation systems, none of the products exhibited cytotoxic or irritant effects. All formulations were classified as non-irritant, supporting their suitability for repeated topical use.

Introduction

The assessment of irritation potential is a critical step in the safety evaluation of cosmetic products, especially those applied to the face and in proximity to the eyes. The delicate nature of ocular tissues requires that formulations demonstrate a high level of tolerability under both intended and incidental exposure conditions.

With increasing regulatory restrictions on animal testing, in vitro methods have become the preferred approach for evaluating irritation potential [2]. Among these, the agarose diffusion cytotoxicity assay is a recognized method for screening the cytotoxic potential of cosmetic formulations [1,3].

This method is based on the diffusion of test substances through a semi-solid agarose matrix toward an underlying cell monolayer. Cytotoxicity is assessed via MTT reduction, which reflects mitochondrial activity and cell viability [4]. The extent of cytotoxicity is quantified by measuring the diameter of cell lysis zones, providing a reproducible indicator of irritation potential.

The use of L929 mouse fibroblast cells is well established in cytotoxicity testing due to their sensitivity to chemical-induced membrane damage and metabolic disruption [5].

This study presents a comparative evaluation of five finished cosmetic formulations:

  • Face Serum
  • Face Mist
  • Face Cream Light
  • Face Cream Rich
  • Eye Cream

All products were assessed using the same standardized protocol to ensure comparability of results.

Materials and methods

Test Items

All test items were finished cosmetic products tested undiluted (pure):

  • Face Serum
  • Face Mist
  • Face Cream Light
  • Face Cream Rich
  • Eye Cream

These formulations are characterized by complex compositions, including high concentrations of active ingredients and amino acid-based systems.

Test System

Cell line: L929 mouse fibroblasts
Culture medium: Complete DMEM
Incubation conditions:
Temperature: 36–37.5°C
CO₂: 5 ± 1%

Experimental Procedure

The assay was performed using the agarose diffusion method:
Cells were seeded at 2 × 10⁶ cells per 60 mm Petri dish and incubated for 24 hours.
A 1% agarose gel was applied over the cell monolayer.
Test items were applied to sterile filter discs placed on the agarose surface.
Samples were incubated for 24 ± 1 hours.
Cytotoxicity was assessed using MTT staining (0.5 mg/mL).
The diameter of any cell lysis zones was measured in centimeters.
Each product was tested in four independent replicates.

Controls

  • Negative control: DMEM / oil (expected no cytotoxicity)
  • Positive control: 3% sodium dodecyl sulfate (SDS)

Classification Criteria

Mean diameter (cm):
< 2.0 → Low cytotoxicity (non-irritant)
2.0–3.0 → Moderate cytotoxicity (irritant)
≥ 3.0 → High cytotoxicity (strong irritant)

Conclusion

Under the conditions of the agarose diffusion cytotoxicity assay:

  • All tested formulations demonstrated low cytotoxicity (mean diameter = 0.0 cm)
  • No ocular irritation potential was observed
  • All products were classified as non-irritant

Importantly, this favorable safety profile was observed despite the presence of high levels of active ingredients and complex formulation systems, supporting their suitability for consistent topical skincare use.

Testing Eye Safety Results

All tested formulations showed identical outcomes, with no detectable cytotoxicity.

Product Mean Diameter (cm) Classification
Face Serum 0.0 cm Non-irritating
Face Mist 0.0 cm Non-irritating
Face Cream Light 0.0 cm Non-irritating
Face Cream Rich 0.0 cm Non-irritating
Eye Cream 0.0 cm Non-irritating

Controls

Negative control: 0.0 cm

Positive control (3% SDS): 2.1 cm

Graph
Result Image

Results Discussion

All five cosmetic formulations demonstrated no detectable cytotoxic effects, indicating excellent cellular compatibility under the conditions of the assay. The agarose diffusion method allows controlled exposure of cells to diffusing compounds and provides a reliable model for assessing irritation-related cytotoxicity [3]. The use of MTT staining enables detection of mitochondrial activity, which is a key indicator of cell viability [4].

The positive control (SDS) consistently produced moderate cytotoxicity, confirming assay sensitivity and validity. SDS is a well-characterized irritant commonly used in validation of in vitro irritation models [6].

A notable aspect of this study is that all formulations contain high levels of active ingredients, including a full spectrum of amino acids and complex multifunctional systems. Such compositions may theoretically increase the risk of irritation due to enhanced biological activity and potential interactions at the cellular level [7].

However, the absence of cytotoxic effects demonstrates that:

  • The formulations are well balanced despite high active content
  • Amino acid complexes contribute to good biocompatibility
  • Cellular tolerance is maintained even under concentrated exposure conditions

Amino acids are known to support skin barrier function, hydration, and cellular metabolism, and are generally associated with high tolerability in topical formulations [8].

These findings support the suitability of the tested products for repeated and long-term topical use, including application to sensitive areas such as the periocular region.

Regulatory and Ethical Compliance

The study was conducted in accordance with:

  • OECD Principle of Good Laboratory Practice (GLP)
  • Directive 2004/10/EC
  • Official French method for cosmetic analysis (1999)

References

  1. Journal Officiel de la République Française (1999). Arrêté du 27 décembre 1999 – Méthode officielle d’évaluation du potentiel irritant par diffusion sur gel d’agarose.
  2. OECD (2019). Guidance Document on Good In Vitro Method Practices (GIVIMP).
  3. Roguet R., Cohen C. (1997). Toxicology in Vitro, 11(3), 275–284.
  4. Mosmann T. (1983). Journal of Immunological Methods, 65, 55–63.
  5. ISO 10993-5 (2009). Biological evaluation of medical devices – In vitro cytotoxicity.
  6. Basketter D.A. et al. (2004). Toxicology in Vitro, 18, 231–236.
  7. Draelos Z.D. (2018). Dermatologic Therapy, 31, e12643.
  8. Rawlings A.V., Harding C.R. (2004). Dermatologic Therapy, 17, 43–48.