OECD Test Guideline 439 describes an in vitro method for evaluating the skin irritation potential of chemicals using a reconstructed human epidermis (RhE) test system. Skin irritation is defined as reversible damage to the skin following exposure to a substance or mixture, and the assay can be used for hazard identification of skin irritants in accordance with the applicable UN GHS classification framework.

The test uses a three-dimensional reconstructed human epidermis model composed of non-transformed human-derived keratinocytes cultured to form a multi-layered, differentiated structure that closely represents the upper layers of human skin. The model contains organized basal, spinous and granular layers together with a multi-layered stratum corneum.

The test chemical is applied topically to the RhE model, and irritation potential is assessed based on chemicalinduced tissue damage. Cell viability is measured through the enzymatic conversion of MTT into a coloured formazan product, which is quantified following extraction from the tissue. Chemicals that reduce tissue viability to the defined threshold level of ≤ 50% are identified as irritants under UN GHS Category 2, while chemicals producing viability above the threshold may be considered non-irritants depending on the applicable regulatory framework.

Vipragen Biosciences offers in vitro skin irritation testing in accordance with OECD TG 439 using reconstructed human epidermis-based test methods as part of its in vitro safety assessment services.