The Rat Skin Transcutaneous Electrical Resistance (TER) Test
The rat skin transcutaneous electrical resistance (TER) test can be used to determine the skin corrosion potential of test chemicals including substances and mixtures without the use of living animals. Whilst described as an in vitro procedure, it can be more correctly defined as an ex vivo method as it requires the use of skin discs excised from a humanely killed young rat. Chemicals that are corrosive to skin are known to produce a loss of normal stratum corneum integrity and barrier function, and this is measured as a reduction in skin TER in a simple two-compartment test system in which the skin discs serve as the separation between the compartments. A dye-binding step allows identification of false-positive results that may occur due to increase in ionic permeability of the skin which is not due to physical destruction of the stratum corneum, such as by some surfactants and neutral organics. The test method can be used to assess solids, liquids, waxes and pastes which are applied directly to the epidermal surface of three skin discs for up to 24 h before determination of the TER using a Wheatstone bridge apparatus. A reduction in the TER below a threshold level of 5 kΩ is indicative of skin corrosion unless demonstrated otherwise in the dye-binding step. Positive and negative controls are included in each study.
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