The OECD 439 In Vitro Skin Irritation test, or Reconstructed Human Epidermis Test, is used to assess the potential for skin irritation occurring after topical exposure to a test article. Previously, this type of testing typically involved the use of laboratory animals. However, this in vitro alternative uses a three-dimensional RhE model comprised of non-transformed human-derived epidermal keratinocytes, cultured to form a multilayered, highly differentiated model of human epidermis. The study design follows the current OECD 439 guideline entitled “In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method (2020)” and can be performed in accordance with Good Laboratory Practices.

Chemical-induced skin irritation occurs due to a cascade of events that ultimately result in the destruction of keratinocytes and other skin cells. These damaged cells then react by releasing inflammatory mediators, and causing a localized inflammatory response at the site of exposure.

The RhE-based test method evaluates the extent of cell/tissue damage by quantifying cell viability. After extraction from the tissues, cell viability is measured using an enzymatic conversion of a vital dye (MTT) into a blue formazan salt. A decrease in cell viability below defined threshold levels thus identifies the test article in question as an irritant chemical.

Typically 1-2 mL or 1-2 grams of test article are required.  This test is performed in compliance with Good Laboratory Practice Regulations.

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