In the context of regulatory hazard classification and labeling, Skin Irritation is defined as the generation of reversible damage to the skin after a defined chemical exposure. The Skin Irritation Test (SIT) is an in-vitro non-animal test designed to identify chemicals and mixtures (UN GHS Category 2 Skin Irritant 1) that may cause moderate skin irritation and to distinguish BM GHS Category 2 Skin Irritants from BM. GHS 3 does not require classification for mild irritants as well as skin irritation potential.

United Nations (UN) Globally Harmonized System of Classification and Labeling of Chemicals (GHS)

This test method is useful for regulatory classification and labeling of chemicals and mixtures, and depending on regulatory jurisdiction and framework, test results can be used independently or support the weight of an evidence approach. In vivo skin irritation is caused by chemically induced cell damage and subsequent inflammatory cascade, this test method provides a mechanically appropriate measure of cell viability in reconstructed human epidermis (RhE) tissues after a single topically applied chemical treatment compared to tissues treated with negative control. It provides. Chemicals that reduce relative viability to ≤P are classified as irritants (and potentially corrosive), while those that result in relative viability will not be classified as skin irritants according to UN GHS Category 2.

EUROLAB has extensive expertise with a wide range of reconstructed skin-based protocols and has participated in preliminary validation and validation studies leading to the adoption of the OECD Test Guideline 439: In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method (TG 439).

NOTE: Since this test method does not distinguish between the UN GHS 1 and 2 categories, an irritant prediction by this test method should be followed by a potential skin corrosion test using any of the approved corrosion test methods. 1) Corrositex Membrane Barrier Time Monitor Corrosion Test Method and 2) In Vitro Skin Corrosion Test Using Reconstructed Human Epidermia (RhE) Model

Various other protocols are available to assess possible skin irritation to support product development, product management, candidate formulation selection and other non-regulatory applications, and can provide skin irritation potential ranking. Several protocols allow the evaluation of light formulations:

1) Time Toxicity ET 50 Screening protocol and

2) Cytokine Expression Test for Light Products and for medium to corrosive products and mixtures:

3) In Vitro Skin Irritation / Corrosion Screen

3D reconstructed human epidermis (RhE) models such as EpiDerm (MatTek Corp.), epiCS (CellSystems), LabCyte EPI-MODEL (Japan Tissue Engineering Co., Ltd) and EpiSkin and SkinEthic RHE (EpiSkin SA) are organotypic in vitro models of human epidermis. These test materials can be used in a variety of assays to assess dermal irritation, erosion, cytotoxicity, phototoxicity and / or anti-inflammatory potential. Tissue viability is determined using vital dye MTT (3- (4,5-Dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide). Reduction of MTT in tissues treated with test material is expressed as a percentage of cultures treated with negative control.

EpiDerm, epiCS, LabCyte EPI-MODEL, and EpiSkin and RHE tissue models are made from human epithelial cells cultured on specially designed cell culture inserts. Cells differentiate to form a fully differentiated epidermis complemented by a functional stratum corneum (see image below). An advantage of using 3-D RhE tissues is that the test materials are applied topically without dilution at full formulation strength, so that most forms of test materials can be applied to the cultures in such a way that they occur in vivo.