In vitro skin sensitisation testing

Traditionally, skin sensitisation testing has been conducted using animal-based methods, but fully validated in vitro tests are now available. XCellR8 is one of only a handful of laboratories worldwide to offer all three tests currently recommended for compliance with a range of legislation including REACH and the CLP Regulation, in entirely animal-free conditions.

The three tests reflect distinct Key Events in the recently-defined Adverse Outcome Pathway (AOP) for human skin sensitisation.

Direct Peptide Reactivity Assay (DPRA) (OECD Test Guideline 442c)

  • Represents Key Event 1 – the “molecular initiating event” of binding to skin proteins

KeratinoSens™ (OECD Test Guideline 442d)

  • Represents Key Event 2 – activation of skin cells (keratinocytes) in the epidermis

h-CLAT (OECD Test Guideline 442e)

  • Represents Key Event 3 – activation of the local immune response via dendritic cells in the epidermis

The tests are fully accepted at a regulatory level to support discrimination of Skin Sensitisers and Non-Sensitisers in accordance with the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS).

Current regulatory guidance for in vitro skin sensitisation testing is to adopt the “2 out of 3” approach, whereby 2 positive results out of the 3 tests (OECD TGs 442c, 442d and 442e) results in classification as a Skin Sensitiser.

In some circumstances, not all tests are appropriate – please get in touch if you’re not sure.

XCellR8 is also the sole global distributor for the newly available GARD®skin Animal-Product-Free – a human genomic screen as an alternative to the h-CLAT method for Key Event 3, in which animal serum has been replaced with human serum. GARD®skin is currently on the path to regulatory acceptance as an OECD Test Guideline and is the first in vitro skin sensitisation test to be validated for the prediction of potency. The Animal-Product-Free adaptation can also be used to support ‘vegan tested’ claims.


The skin sensitisation tests are appropriate for compliance with a range of legislation including:

  • REACH (EC 1907/2006)
  • The CLP Regulation (EC 1272/2008)
  • The Biocidal Products Regulation (EC 528/2012)
  • The Plant Protection Products Regulation (EC 1107/2009)
  • The Cosmetics Regulation (EC 1223/2009)

The three tests also provide a useful screen at non-regulatory stages of product development.


The standard KeratinoSens™ and h-CLAT tests include the use of animal-derived components in the test system, such as serum and antibodies. To provide our clients with truly animal-free tests, XCellR8 has adapted the methods to animal product-free conditions. Proficiency testing as per OECD Test Guidelines 442d and 442e has demonstrated our successful classification of a panel of reference chemicals in terms of skin sensitisation potential. ECHA (the European Chemicals Agency) has confirmed that the adapted tests are suitable for submissions under REACH.

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