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OECD TG 439

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OECD TG 439

OECD TG 439, OECD-Prüfrichtlinien für die Prüfung von Chemikalien, Abschnitt 4 (Gesundheitliche Auswirkungen) im Rahmen der „In-vitro-Hautreizung: Testmethode mit rekonstruierter menschlicher Epidermis (RhE)“, d. h. „In-vitro-Hautreizung: Testmethode mit rekonstruierter menschlicher Epidermis (RhE)“. Er wurde erstmals im Jahr 2010 verabschiedet, 2015 aktualisiert und durch nachfolgende Überarbeitungen wurde sein Anwendungsbereich erweitert. Im Rahmen der gesundheitlichen Auswirkungen handelt es sich um einen In-vitro- Toxizitätstest und um einen ansatz, der ohne Tierversuche auskommt.

Note on regulatory status: TG 439 is widely used in the EU under the CLP Regulation (EC 1272/2008) and REACH, as well as within the framework of the ban on animal testing for cosmetic products. The current version and the latest revisions to the scope of application should be checked against official OECD sources before commencing the study.

The basic principle of the test is as follows:

  • The test substance is applied topically to the surface of reconstructed human epidermis (RhE) tissue. RhE is a multilayered and differentiated epidermal model consisting of human keratinocytes (e.g. validated models such as EpiSkin, EpiDerm, SkinEthic RHE, LabCyte EPI-MODEL, epiCS).
  • Die Expositionsdauer hängt vom physikalischen Zustand der Testsubstanz ab: bei Flüssigkeiten in der Regel 15 Minuten, bei Feststoffen in der Regel 4 Stunden.
  • Once the exposure time has elapsed, the test substance is removed from the tissue (by washing) and the tissue is incubated for a further specified period.
  • Cell viability is measured using the MTT assay. MTT is converted into formazan salt by the mitochondrial dehydrogenases of living cells; the amount of formazan produced is proportional to the number of living cells.
  • The percentage of cell viability is calculated in comparison with the negative control tissues.
  • The result is interpreted using validated cut-off values: if the viability is ≤ 50 per cent, the substance is classified as irritant (Category 2); if it is > 50 per cent, it is considered non-irritant.
  • If necessary, validation can be carried out using a second RhE model or additional markers (e.g. IL-1α and IL-8 release).

TG 439 forms part of the sequential testing strategy. First, the physicochemical properties (e.g. pH ≤ 2 or ≥ 11.5) and in vitro corrosivity tests (TG 430, TG 431) are assessed; for non-corrosive substances, the assessment of irritancy is carried out in accordance with TG 439. This approach forms part of the sequential strategy defined in OECD TG 404 and largely renders in vivo tests unnecessary.

The key parameters reported in the study are:

  • The RhE model used, as well as manufacturer and validation information
  • Physical state of the test substance (liquid/solid) and the amount used
  • Duration of exposure (15 minutes for liquids; 4 hours for solids) and conditions of use
  • After exposure: incubation period and washing procedure
  • Cell viability (%) (for each parallel tissue sample) and mean value
  • Results of the positive (e.g. SDS, a chemically recognised irritant) and negative controls
  • Confirmation that the checks meet the validity criteria
  • Result: irritant (Category 2) / non-irritant – assessment and justification
  • Data on measurement uncertainty and repeatability

What is the purpose of the examination?

OECD TG 439 is being carried out for the following scientific and regulatory purposes:

  • Determination of dermal irritation potential: assessment of a substance’s potential to cause reversible irritation following skin contact
  • GHS/CLP classification: Determining whether the substance is to be classified as a skin irritant, Category 2, and identifying the labelling requirements (H315)
  • Animal welfare (3Rs): As an alternative to the in vivo Draize skin irritation test (TG 404), the use of animals is avoided; compliance with the ban on animal testing for cosmetic products
  • Step-by-step testing strategy: Completion of the in vitro irritation assessment following corrosivity tests (TG 430, TG 431)
  • Support with regulatory documentation: assistance with safety assessments under REACH, for biocides, plant protection products, cosmetics and industrial chemicals
  • Product safety and labelling: establishing warning notices and safety measures to protect consumers and staff
  • Formulation and Materials Development: Early identification of new products and materials
  • Approach to weight of evidence: contribution to the holistic assessment of the substance in conjunction with other physicochemical, in vitro and in vivo data

OECD TG 439 provides only an assessment of irritation; corrosivity (TG 430, TG 431), sensitisation (TG 442 series), systemic toxicity and phototoxicity do not fall within the scope of this standard. Furthermore, RhE models do not fully reflect the full thickness of human skin (including the dermis) nor do they fully reflect systemic reactions. The results should be interpreted in the context of the substance’s physicochemical properties and other toxicological data.

At NanoTest, we carry out in vitro skin irritation tests in accordance with OECD TG 439 with scientific rigour, within the framework of our accredited laboratory infrastructure and our quality management system.

For information on planning a sequential testing strategy, selecting the RhE model, the application and measurement strategy, sample acceptance criteria, the testing schedule and the reporting procedures for your inin vitro skin irritation tests in accordance with OECD TG 439, please feel free to contact NanoTest.

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