Facial action coding system (FACS)

Tools for the

Facial action coding system (FACS)

Many researchers code muscle movements to learn more about how and why the face moves. They use the Facial Action Coding System which provides them with a technique for the reliable coding and analysis of facial movements and expressions.

The Facial Action Coding System (FACS), first developed by Paul Ekman and Wallace Friesen in 1978 and revised by Ekman, Friesen, & Hager in 2002, is a comprehensive, anatomically-based system for describing anatomical movement of the face.

Tools for the Facial action coding system (FACS)
Action Units are part of FACS

FACS coding

FACS coders describe every observable change in facial movement on the basis of Action Units (AUs). They indicate which AUs moved to produce the changes observed in the face. This makes FACS coding quite objective.

In scoring, it will be necessary to apply slow motion and frame-by-frame viewing to identify the AUs that occur, always alternating with real time viewing. As such, FACS coding is very time intensive.


Automatically code facial actions

FaceReader™, the software for automatic recognition and analysis of facial expressions, offers you reliable automated facial action coding, which saves you valuable time and resources. 

When an action is active, its intensity is displayed in 5 categories. Output will be presented to you on this scale with different colors and can be exported for further analysis in Excel, The Observer® XT, or another program of your choice.

FaceReader analyzes left and right Action Units (AUs) separately. This unique feature distinguishes the intensity of the active muscles at the left and the right side of the face.

FaceReader shows an overview of action units


FaceReader is used worldwide at more than 1,000 universities (including 6 out of 8 Ivy League universities), research institutes, and companies in many markets such as psychology, consumer research, user experience, human factors, and neuromarketing.


Free white paper

Facial Action Coding System (FACS)

Coding facial actions is used in many different settings, for example in science, teaching, and by animators as well. It enables a greater awareness to subtle facial behaviors.

Download the free white paper and find out: 

  • how to measure AUs objectively
  • which tools will provide you results
  • all the benefits of using FACS

What Facial Action Units look like

Recent advances in computer vision have allowed for reliable automated facial action coding. Below you can see the 20 Action Units offered in FaceReader as well as some frequently occurring or difficult action unit combinations. 

Some images have been zoomed in on the area of interest to explicitly show what muscle movement corresponds to the specific Facial Action Unit.

AU 1. Inner Brow Raiser

Contributes to the emotions sadness, surprise, and fear, and to the affective attitude interest. Muscular basis: frontalis (pars medialis).

AU 2. Outer Brow Raiser

Contributes to the emotions surprise and fear, and to the affective attitude interest. Frontalis (pars lateralis) is the underlying facial muscle.

AU 4. Brow Lowerer

Contributes to sadness, fear, and anger, and to confusion. Muscles: depressor glabellae, depressor supercilii, and corrugator supercilii.

AU 5. Upper Lid Raiser

Contributes to surprise, fear, and anger, and to interest. Muscular basis: levator palpebrae superioris, and superior tarsal muscle.

AU 6. Cheek Raiser

Contributes to the emotion happiness. Orbicularis oculi (pars orbitalis) is the underlying facial muscle.

AU 7. Lid Tightener

Contributes to the emotions fear and anger, and to confusion. Orbicularis oculi (pars palpebralis) is the underlying facial muscle.

AU 9. Nose Wrinkler

Contributes to the emotion disgust. Levator labii superioris alaeque nasi are the underlying facial muscles.

AU 10. Upper Lip Raiser

Levator labii superioris, caput infraorbitalis are the underlying facial muscles.

AU 12. Lip Corner Puller

Contributes to the emotion happiness and contempt when the action appears unilateraly. Muscular basis: zygomaticus major.

AU 14. Dimpler

Contributes to the emotion contempt when the action appears unilateraly, and to boredom. Buccinator is the underlying muscle.

AU 15. Lip Corner Depressor

Contributes to the emotions sadness and disgust, and to confusion. Depressor anguli oris is the underlying muscle.

AU 17. Chin Raiser

This Action Unit contributes to the affective attitudes interest and confusion. The underlying facial muscle is mentalis.

AU 18. Lip Pucker

The underlying facial muscles are incisivii labii superioris and incisivii labii inferioris.

AU 20. Lip Stretcher

Contributes to the emotion fear. The underlying facial muscle is risorius w/ platysma.

AU 23. Lip Tightener

Contributes to the emotion anger, and to the affective attitudes confusion and boredom. Muscular basis: orbicularis oris.

AU 24. Lip Pressor

This Action Unit contributes to the affective attitude boredom. The underlying facial muscle is orbicularis oris.

AU 25. Lips Part

The muscular basis consists of depressor labii inferioris, or relaxation of mentalis or orbicularis oris.

AU 26. Jaw drop

Contributes to the emotions surprise and fear. Muscular basis: masseter; relaxed temporalis and internal pterygoid.

AU 27. Mouth Stretch

The underlying facial muscle are pterygoids and digastric.

AU 43. Eyes Closed

Contributes to the affective attitude boredom. The muscular basis consists of relaxation of Levator palpebrae superioris.

Combinations of action units

AU 1 - 2 - 4

Contributes to the emotions fear and can be recognized by the wavy pattern of the wrinkles across the forehead.

AU 1 - 2

Contributes to the emotion surprise and can be recognized by a smooth line formed by the wrinkles across the forehead.

AU 1 - 4

Contributes to sadness. Recognizable by a wavy pattern of the wrinkles in the center of the forehead. Eye-brows come together and up.

AU 4 - 5

Contribute to the emotion anger.

AU 6 - 12

Contributes to happiness. Notice the wrinkles around the eyes caused by cheek raising, also know as the "Duchenne Marker".

AU 10 - 25

Contributes to the emotion disgust. When AU10 is activated intensily, it causes the lips to part as the upper lip raises.

AU 18 - 23

Often confused as solely AU18. Notice the lips almost appear to be pulled by a single string outward (AU18) and then tightened (AU23).

AU 23 - 24

The AUs marking lip movements are often the hardest to code. The lips are being pushed together (AU24) and tightened (AU23)


Non-verbal behavior studies

Research has demonstrated that most human communication is non-verbal, and only measurable by means of observations. Methods range from straightforward live observations with a handheld device to elaborate lab studies, and from video analysis with The Observer XT to automatic facial expression recording with FaceReader.


Customer quote

"The Observer XT is an excellent tool to code the complexity of facial expressions, their on- and offset, their time course and their changing intensities."

Dr. Miram Kunz|University of Augsburg, Germany


Interesting publications

A diverse collection of scientific articles citing Noldus products are published in renowned journals each week. The following list is only a small selection of scientific publications about facial action coding system and/or facial expression analysis.

  • Ekman, P.; Friesen, W. V.; Hager, J. C. (2002). Facial action coding system: The manual on CD-ROM. Instructor’s Guide. Salt Lake City: Network Information Research Co.
  • Lewinski, P.; Fransen, M. L.; Tan, E.S.H. (2014). Predicting Advertising Effectiveness by Facial Expressions in Response to Amusing Persuasive Stimuli. Journal of Neuroscience, Psychology, and Economics, 7, 1-14.
  • Kunz, M.; Lautenbacher, S. (2014). The faces of pain: A cluster analysis of individual differences in facial activity patterns of pain. European Journal of Pain, https://doi.org/10.1002/j.1532-2149.2013.00421.x.
  • Schalk, J.; Hawk, S.; Fischer, A. & Doosje, B. (2011). Moving Faces, Looking Places: Validation of the Amsterdam Dynamic Facial Expression Set (ADFES). Emotion, 11 (4), 907-920. https://doi.org/10.1037/a0023853.

Relevant blogs


The role of mimicry in the development of social communication

Children learn from interacting with others, especially their parents. For example, reproducing the emotions that others express is part of that.

Entrepreneurs’ facial expressions & emotional contagion during investor pitches

What is the influence of emotions in a decision-making process? Dinkla and Liebregts wondered if displaying joy and emotional mimicry play a role during pitches.

The facial action coding system in infant behavior research

Non-verbal behavior is very important in analyzing interpersonal communication. Think about waiving your arms when explaining something, nodding your head, or frowning.
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