National Toxicology Program

National Toxicology Program

Immunotoxicity: Identification of Substances That May Cause Allergic Contact Dermatitis

Substances with the potential to cause allergic contact dermatitis (ACD) are skin sensitizers; the process by which they cause ACD is skin sensitization.

Read article "Allergic Contact Dermatitis: What Is It, and Why Should I Care About It?"

Integrated Testing Strategies to Identify Potential Skin Sensitizers

The biological pathway leading to skin sensitization is well characterized and thus is a promising area for the near-term development of testing strategies that eliminate the use of animals. ICCVAM and NICEATM scientists developed integrated testing strategies based on this pathway, using chemical property information and non-animal test data as input for their models. These non-animal approaches can be used to predict either outcomes for the standard animal test to identify potential skin sensitizers or human skin sensitization hazard.

Electrophilic Allergen Screening Assay (EASA)

Binding of a chemical to skin proteins is the first step in the development of ACD. The EASA is a chemical assay that measures light absorbance or a fluorescent signal in proportion to a chemical’s tendency to bind to proteins.

The EASA was nominated to ICCVAM in 2012 to evaluate its usefulness in identifying potential skin sensitizers. Four ICCVAM member agencies are participating in a validation study of the EASA that is in progress and is expected to be completed by the end of 2017.

Workshop on Best Practices for Assessing the Potential for Chemically Induced Allergic Contact Dermatitis

NICEATM and ICCVAM organized a workshop in 2011 to provide stakeholders with information about ICCVAM-recommended alternative test methods for assessing ACD hazard potential. The workshop reviewed best practices for testing chemicals and products for ACD potential using methods and approaches that replace, reduce, and refine animal use.

ICCVAM Evaluations of the Murine Local Lymph Node Assay (LLNA)

ICCVAM has evaluated several versions of the LLNA. Compared to guinea pig methods originally used to identify skin sensitizers, the LLNA:

  • Reduces the number of animals required for testing
  • Requires less time to perform
  • Provides dose-response information
  • Eliminates the pain and distress associated with an allergic response in animals

Data from analyses of the LLNA conducted on behalf of ICCVAM by NICEATM are available to interested stakeholders as a reference for developing and evaluating alternative approaches to testing and assessment that replace, reduce, or refine the use of animals for identification of potential skin sensitizers.


Database users please note:

  • The Excel spreadsheet contains three pages: (1) data, (2) references, and (3) abbreviations.
  • The database includes data published through 2010.
  • These data have been extracted from published and unpublished data sources with permission. Users of this database should consult the original data source for questions regarding data quality and/or authenticity.
Use of the LLNA for Potency Categorization

In 2007, the U.S. Consumer Product Safety Commission (CPSC) requested that NICEATM and ICCVAM assess the validation status of new versions and applications of the LLNA. In response, ICCVAM evaluated the use of the LLNA for potency categorization of chemicals that cause ACD in humans. ICCVAM concluded that the LLNA can be used to categorize substances as strong skin sensitizers (Globally Harmonized System of Classification and Labelling of Chemicals Subcategory 1A). However, substances that are not identified as strong sensitizers using the LLNA require additional information to categorize them as other than strong sensitizers (Globally Harmonized System of Classification and Labelling of Chemicals Subcategory 1B).

Nonradioactive Versions of the Murine Local Lymph Node Assay

ICCVAM made recommendations to Federal agencies on the use of two nonradioactive versions of the LLNA. The availability of LLNA methods that do not use radioactivity allows more institutions to take advantage of the animal welfare and environmental benefits of the LLNA.

Applicability Domain for the Murine Local Lymph Node Assay

Following a peer review evaluation of the LLNA in 1998 (see last paragraph below), ICCVAM recommended the LLNA as a valid alternative to guinea pig test methods for assessing ACD hazard potential for most testing situations. The CPSC nomination noted above requested that NICEATM and ICCVAM evaluate the applicability of the LLNA for testing formulations, metals, substances in aqueous solutions, and other products with the expectation that a wider applicability domain for the LLNA would enable wider use. ICCVAM recommended that the LLNA be used to test any chemical or product for ACD hazard potential unless the chemical or product to be tested has properties that may interfere with the ability of the LLNA to detect sensitizing substances.

Performance Standards for the Murine Local Lymph Node Assay

ICCVAM prepared performance standards for the LLNA that can be used to evaluate the accuracy and reliability of new versions of the LLNA. These performance standards represent a set of internationally harmonized standards for the conduct of the LLNA (essential test method components, a minimum list of reference substances, and accuracy and reliability criteria). The performance standards also include a updated LLNA test method protocol that reduces animal use by 20% by decreasing the minimum number of animals per dose group from five to four compared to the original ICCVAM‑recommended protocol.

Reduced Murine Local Lymph Node Assay

One of the LLNA modifications evaluated by NICEATM and ICCVAM in response to the CPSC nomination was the “reduced” LLNA (rLLNA). When used to test a substance for the potential to cause ACD, the rLLNA uses fewer animals than the LLNA to provide a “yes-no” result. ICCVAM has recommended the use of the rLLNA rather than the standard (multidose) LLNA when a negative result is expected or when dose–response information is not required. Since the rLLNA uses only a single high-dose group along with concurrent negative and positive control groups, adoption of the rLLNA reduces the number of animals needed for each test by 40% compared to the standard LLNA.

ICCVAM Evaluation of the Validation Status of the Murine Local Lymph Node Assay

In 1998, NICEATM convened an independent peer review panel to review the validity of the LLNA as an alternative to guinea pig tests for assessing ACD hazard potential. The panel concluded that the LLNA

  • Is a valid alternative to currently accepted guinea pig test methods
  • Reduces the number of animals required for testing
  • Eliminates the pain and distress associated with an allergic response
  • Requires less time to perform
  • Provides dose–response information
NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.