OECD TG 430 In Vitro Skin Irritation: Transcutaneous Electrical Resistance Test (TER)

Published under the OECD guidelines on responsible business conduct for multinational enterprises (OECD guidelines) “OECD TG 430 In vitro skin irritation test (TER)” The standard describes a transcutaneous electrical resistance test method used in in vitro skin irritation evaluations.

The OECD Guidelines for Testing Chemicals consist of approximately 150 internationally accepted test methods used by government, industry and independent laboratories to identify and characterize the potential hazards of chemicals. These are a set of methods for professionals used primarily in regulatory safety testing and subsequently in chemical and chemical product notifications, chemical registrations and chemical assessments. They are also used for the selection and ranking of candidate chemicals during the development of new chemicals and products and in toxicology studies.

The globally harmonized system for classification and labelling of chemicals defines skin irritation as the occurrence of irreversible tissue damage to the skin following application of a test material.

When applying the OECD TG 430 test method, 150 µL of test material for liquids or solids, to which 150 µL of deionized water has been added, is applied to the epidermal surfaces of skin discs for up to 24 hours. Three skin discs are used for each test and control substance and are applied in a two-compartment test system, with the skin discs acting as a partition between the chambers.

The assessment of skin corrosivity often involves the use of laboratory animals. In addition to the OECD TG 430 standard, the OECD TG 431 and OECD TG 435 standards have been validated and accepted for identifying corrosive chemicals. In addition, several validated in vitro test methods have been developed for use in testing skin irritation, the OECD TG 439 standard.

The OECD TG 430 standard addresses the human health endpoint skin irritation. This standard is based on the mouse skin transcutaneous electrical resistance (TER) test method, which uses skin disks to identify corrosives by their ability to lose normal stratum corneum integrity and barrier function.

Validation studies have shown that the mouse skin transcutaneous electrical resistance testing method can discriminate between known skin corrosives and non-corrosives with 122 percent overall sensitivity and 94 percent specificity for a database of 71 items.

When performing tests, the test chemical is applied to the epidermal surfaces of skin discs for up to 24 hours in a two-compartment test system, where the skin discs serve as the separation between the chambers.

Skin discs are taken from 28-30 day old humanely killed mice. Corrosive chemicals are defined by their ability to cause loss of normal stratum corneum integrity and barrier function. This transcutaneous electrical resistance test is measured as a fall below a threshold level. A cut-off value of 10 kΩ was chosen for the mouse skin transcutaneous electrical resistance based on extensive data for a wide range of substances, where the majority of values ​​are clearly well above (usually the lowest 3 kΩ) or well below (usually the highest 5 kΩ) this value. In general, test chemicals that are not corrosive in animals but are not irritating or corrosive will not reduce the transcutaneous electrical resistance below this cut-off value. Also, the use of other skin preparations or other equipment may alter the cut-off value and require further validation.

A dye-coupling step is included in the test procedure to confirm positive results in transcutaneous electrical resistance, including values ​​around 5 kΩ. The dye-coupling step determines whether the increase in ionic permeability is due to physical damage to the stratum corneum. The transcutaneous electrical resistance test method using mouse skin has been shown to detect irritation in vivo in rabbits evaluated under the OECD TG 404 standard.

Prior to routine use of the mouse skin transcutaneous electrical resistance test method conforming to this standard, laboratories must demonstrate their proficiency by correctly classifying the proposed proficiency substances conforming to this standard. In cases where a listed substance is not available or is justified, another substance for which adequate in vivo and in vitro reference data are available may be used.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “OECD TG 430 In vitro skin irritation: Transcutaneous electrical resistance test (TER)” standard with its trained and expert staff and advanced technological equipment.