Toxicity Testing: Animals and Alternatives

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This topic addresses the general approaches used to evaluate medicines, cosmetics, food additives, household products and other chemicals that workers and consumers are exposed to in their daily lives.


Why is testing necessary?

The safety of chemicals must be evaluated to protect the health of the public and the environment.  Veterinary products are also tested to ensure safe use of products for our household pets and livestock.  Testing is required by government regulatory agencies and specific methods are recommended for a comprehensive evaluation before release to the consumer market.    Further testing of environmental samples using different approaches and methods may also be necessary where complex mixtures of small amounts of substances may have a different effect that could not be predicted from the behavior of individual substances (e.g. synergistic effects).


Medicines are examined in human beings according to strict ethical rules; however, strict prohibitions in effect worldwide restrict giving any products to humans without first testing them in appropriate model systems.   However, many chemicals in products that consumers will be exposed to, including pesticides, cleaners and other chemicals used in the production of consumer products including toys, clothing, building materials and furniture, cannot be tested directly in humans before release in the market.



Important role for animal testing – historically and now.

Many sources cite the post-WWII (1948) Nuremberg Code as the beginning of strict prohibitions worldwide against unethical experimentation on human beings.    The Tuskegee Syphilis Experiment, in which prisoners were infected with syphilis without their knowledge and left untreated to observe progression of the disease, further underscored the need for strict compliance with ethical testing methods, including no testing in human subjects without informed consent.


Meanwhile, animal care and welfare policies and practices focused on ensuring humane and standardized treatment.   The “3Rs” became widely adopted during further development of animal testing policies and practices.  First described in 1959 by William Russell and Rex Burch, humane techniques were classified as replacement, reduction, and refinement.  Now commonly known as the 3Rs, these principles are explained further below in the section on current practices.   In 1963 the first edition of “The Guide for the Care and Use of Laboratory Animals” was published.  This guidance helped to further standardize acceptable procedures for all biomedical researchers.


Many people do not fully understand the advantages and limitations of using animal models, and why scientists continue to use animals in research.  Use of animals as surrogates is most appropriate and successful when the anatomical, physiological, and biochemical makeup of the laboratory animal, and how it compares to humans, is well understood.    Lab animals are clearly not simply smaller human beings!  However, our similarities to a rat, for example, are far greater than our differences.   There is overwhelming evidence that use of laboratory animals is justified from a scientific perspective because it is effective at determining some degree of safety before humans are allowed to take medications.  Nevertheless the use of animals remains a controversial approach.


What the general public also may not know is that although toxicologists understand the purpose and value of animal testing, many still struggle to some extent with the ethical dilemma of using animals in their work.   Some may opt instead to focus solely on questions that can be answered by other means.


Current regulations and standards

As explained above, regulatory agencies require that model systems be used before human testing can occur.   These regulations vary by country and region.  Any detailed discussion about the differences and the consequences of this is beyond the scope of this topic.  Suffice it to say that closer alignment of rules and regulations worldwide has been a major initiative for several decades now—-commonly referred to as “harmonization”—and much progress has been made.


Also, some regulations no longer allow the use of animal testing. This is the case in Europe for cosmetics, including both finished products and their ingredients.   Alternative approaches for evaluating safety of cosmetics are being adopted in the EU, some of which are mentioned later in this topic.


When animals are used, some basic standards for humane and ethical treatment of test animals apply worldwide.  The 3Rs of Russell and Birch are promoted within the entire biomedical research community:

  • Replacement: The use of alternative methods such as isolated cells, reconstructed tissues or software (in silco tools) to predict effects in humans. This approach is now mandatory for the Cosmetics industry in Europe, but it represents a major technical challenge. Several research initiatives have addressed or still are addressing the development of alternative / predictive methods for different purposes.
  • Reduction: When alternative methods are not available, careful considerations should be taken before performing the animal testing and only a minimum number of animals to derived robust information should be used.
  • Refinement: Calls for a humane treatment of the animals when no other possibility exists to obtain information that will guarantee the safe use of the compounds by humans.


Concerning refinement, it is widely understood among toxicologists who use animal that maintaining animal health and wellbeing, providing environmental enrichments, and minimizing stress are all necessary for an accurate understanding of the effects of a substance being evaluated.   In fact, strict compliance standards and rigorous oversight of animal testing are expected in all areas of biomedical research.   At the same time, some standardized test protocols are being refined so as to reduce numbers of animals needed.  Replacements for animal testing are also used increasingly as the models are developed and validated.


The Guide for the Care and Use of Laboratory Animals is also followed and updated regularly to remain consistent with current standards of veterinary care and ethical practices.  (


Some of the available replacements


A huge effort has been made to identify and adopt good alternatives that are recognized and trusted in a regulatory setting.   A few general approaches are mentioned here.  Several websites within the resource section provide a lot more detail on this subject.


  • QSAR: Quantitative Structure Activity Relationships (QSARs) are mathematical models used to predict measures of toxicity based on chemical structure and the characteristics associated with similar chemical structures.
  • Read across: To “read across” is to apply data from a chemical that has been tested for a particular property or effect (for example cancer or reproductive toxicity) to a similar chemical that has not been teste
  • In silico toxicology: “In silico” refers to silicon used in computer chips. Estimates of toxicity are performed using computers.  Supercomputers have expanded possibilities in some areas of toxicology; for example, in genomics that applies computer chip technology to evaluate changes in function in thousands of genes in organisms of interest that may be associated with a disease or chemical exposure.
  • Computational toxicology: Computational toxicology integrates data and other information from a variety of sources to develop mathematical and computer-based models to better understand and predict adverse health effects.
  • In vitro alternatives: “In vitro” meaning “in glass”, originally referring to tests using glass test tubes or Petri dishes.  Readers interested in this topic are encouraged to visit websites referenced below for much more information on this topic.  Briefly, the most famous is the Ames Salmonella mutagenicity test that detects specific types of DNA damage in bacteria exposed to chemicals.  Alterations of the genetic material can lead to cancer; however, not all genotoxic chemicals have the potential to induce cancer in a whole animal, including human beings.  This illustrates a potential concern about in vitro alternatives when an in vitro test falsely reports a chemical to have some effect in a model system when it actually does not have that effect in humans or when tested in animals.  This is commonly known as a ‘false positive’ result.  The converse is also a potential concern; that is, when an in vitro model shows no effect when in fact there is in an intact organism.


Future research needed and what it will take to get us there.

Many web-based and other resources dealing with alternatives to animal testing reflect a very serious commitment to the 3Rs and to developing and validating suitable alternatives.  Research is ongoing to maximize understanding of animal models to ensure that the testing ultimately performed is optimized and eliminate unnecessary testing.   Current replacement models, although suitable for what they can tell us, typically focus on a defined part of the body (e.g., section of skin), or a specific effect (e.g., genotoxicity) that may or may not be reversible as the chemical exposure diminishes and the body repairs itself.  Currently few alternative models provide much information about reversibility of an effect observed.   Research is also ongoing to find new ways to mimic the complexity of a complex organism in a test model and reduce other limitations of model systems.


Establishing validity of any new testing approach is critically important before information obtained using that method can be accepted by regulatory agencies charged with ensuring safety of the general public and our environment.  Establishing validity includes understanding how well that test model predicts a chemical’s behavior in a whole lab animal or a human being.   One example of this is to understand the ‘false positive’ and ‘false negative’ rates and reasons for this in test results from an in vitro model, such as in the Ames test mentioned above.


Development and acceptance of model systems usually takes many years and a significant economic investment.   Much progress has been made, but at the present time few alternative tests can substitute completely for information obtained using live animals.





  • Computational Toxicology (CompTox): A — USEPA research initiative, CompTox  is investigating  new and more efficient ways to address managing the safety of chemicals, one of many intended outcomes to be the elimination of redundant and otherwise unnecessary animal testing:\
  • ICCVAM/NIEHS (Interagency Coordinating Committee on the Validation of Alternative Methods is a permanent committee of the National Institute of Environmental Health Sciences (NIEHS) under the National Toxicology Program Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM).Q&A on alternatives to animal testing



  • Tuskegee Syphilis Experiment: Untreated Syphilis – A U.S. Public Health Service experiment that began in 1939, the study was terminated after unfavorable media coverage exposed unethical practices. Historically significantly because it led to stricter rules about no first testing in humans without prior consent.




Related topic:    Cosmetics Safety