Grimace scales

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Why were the grimace scales developed?

Effective alleviation of pain in laboratory animals depends on the ability to recognise pain and assess its severity. Traditional methods of pain assessment based on monitoring of behaviour and clinical signs (e.g. weight loss) are time consuming and can have other limitations (e.g. the signs observed may not be specific to pain).

Research by Dr Jeffrey Mogil and colleagues, McGill University, has demonstrated that changes in facial expression provide a reliable and rapid means of assessing pain in mice and rats. ‘Grimace scales’ have been developed for these species, based on changes in a number of ‘facial action units’, such as narrowing of the eyes (orbital tightening) or changes in the position and shape of the whiskers.

With funding from the NC3Rs, Dr Matthew Leach, Newcastle University, has demonstrated that these facial action units increase in intensity in response to post-procedural pain, and could therefore be used as part of a clinical assessment; he also developed a rabbit grimace scale. Grimace scales have since been developed for other species.

Where grimace scales are being used to assess pain in real time at the cage/pen side, each animal should be observed for a short period of time to avoid scoring brief changes in facial expression that are unrelated to the animal’s welfare. They should only be used with awake animals. 

VIDEO: Dr Leach discussing methods of pain assessment in animals

Grimace scale posters


Hard copies (currently not available due to COVID)

The NC3Rs has produced A3-sized posters of the mouse, rabbit and rat grimace scales for display in laboratory animal facility rooms and corridors, to help raise awareness about the scales and familiarise staff with the specific facial action units.

Whilst we have previously been able to send hard copies of these posters around the world, we are currently unable to do so due to COVID restrictions. Therefore we are now able to offer downloadable copies, subject to the T&Cs outlined below.

Download terms and conditions

The proper use of a grimace scale poster requires each of the facial action units to be clear and easily discernible. They therefore must be printed by a professional print service at the full A3 size. Further guidance is included in the cover page which should not be removed from the PDF file.

Any requests to reproduce this poster, or to include it in any publications or training materials, should be directed to You should include how, why and where the poster will be used so that we can consider your case for approval. It is helpful to include any associated text, so we can see the context in which the poster will be put.

Copyright notice: These posters and their content are owned by the NC3Rs and its partners. The poster should not be adapted, and the content should not be sold or used to generate income.

Available posters for download

Species Language Download link (PDF)
Mouse English Download the Mouse Grimace Scale in English
Rat English Download the Rat Grimace Scale in English
Rabbit English Download the Rabbit Grimace Scale in English


Download the Mouse Grimace Scale in French


Download the Rat Grimace Scale in French


Download the Rabbit Grimace Scale in French

Additional resources

See the links below for guidance on how to use the grimace scales and research papers that underpin and validate this technique.

Whilst we include the original training manuals for the mouse and rat grimace scales, please note that these focus on transcribing video recordings and validation of the scales for research purposes. Many laboratories instead use the grimace scales as part of their clinical assessments at the cage/pen side, scoring facial expressions in real time.