A visual reference guide for the Facial Action Coding System (FACS) and beyond, featuring action units (AUs) and their corresponding musculature. Designed for animators, modelers, riggers, sculptors, and researchers.
#notFACS indicates actions I have identified and coined that do not exist in FACS. Due to FACS’s original purpose as a facial behavior identification system, FACS lacks documentation for some finer, more nuanced facial movements. To fill this void, I have further defined my own nonFACS movements such as: vertical lip tightener, y-axis dimpler, open-eye blink, etc. If you work on lipsync technology or photoreal characters, these distinctions will be particularly useful.
FOREHEAD AREA & EARS
FACS name
muscle name
expression reference
AU1 – inner brow raiser
frontalis (the medial portion)
AU1 ACTION:Inner brow raiser lifts the medial brow and forehead area.
NOTE 1: Inner brow raiser is variable in wrinkle formation and range. This variability is due to a number of factors, a prominent factor being frontalis muscle variability.
AU2 ACTION:Outer brow raiser lifts the lateral brow and forehead areas.
NOTE: As mentioned with inner brow raiser, outer brow raiser is also variable in wrinkle formation and range. This variability is due to a number of factors, a prominent factor being frontalis muscle variability.
AU4 ACTION:Brow lowerer knits (corrugator supercilii) and lowers (procerus, depressor supercilii, and parts of corrugator supercilii) the brow area and lower central forehead. **Read NOTE below for important considerations.
EARS UP & BACK ACTION:Ears up & back lifts the ears and pushes them back.
NOTE1: This is not a FACS action. I have included this ear movement in the FACS Cheat Sheet, because I observe it happening relatively frequently.
NOTE 2: There are multiple auricular muscles. The superior auricular moves the ears up. The posterior auricular moves the ears back. The anterior auricular the moves ears forward. At present, I cannot separate these movements. The reference here shows posterior auricular + superior auricular movement.
EYE & CHEEK AREA
FACS name
muscle name
expression reference
AU5 – upper lid raiser
levator palpebrae superioris
AU5 ACTION:Upper lid raiser pulls the top eyelid up and back to widen the eyes.
orbicularis oculi (the pretarsal portion of the palpebral area)
OPEN-EYED BLINK ACTION:Open-eyed blink tightens the innermost rings around the eyelids in a circular motion toward the inner eye corners.
NOTE: The pretarsal area is the portion of our orbicularis oculi muscle that is involved with blinking. See more breakdowns here.
AU45 – blink
orbicularis oculi (the pretarsal portion of the palpebral area)**
AU45 ACTION:Blink closes and opens the eyes in a swift, fluid manner.
NOTE: Beyond pretarsal activation, blink also often consists of: (1) relaxation of levator palpebrae superioris and/or (2) forced closure from the preseptal portion of orbicularis oculi.
AU46 – wink
orbicularis oculi
AU46 ACTION:Wink closes one eye, usually with some compression.
NOTE: Unless you are a facial coder conducting behavioral research (and even then, the official FACS Manual lists AU46 – wink as “optional”), the FACS shape for wink is not the most useful. I have included it because other FACS lists include it; however, I find it to be a clunky, unnecessary addition to most shape sets. That being said, orbicularis oculi does deserve better functional breakdowns beyond cheek raiser, blink, and lid tightener – but wink is not the way to go. In the near future, I will post a functional breakdown of orbicularis oculi. Sign up for monthly post updates to keep tabs on the latest content and breakdowns.
AU9 ACTION:Nose wrinkler lifts the sides of the nose, nostrils, and central upper lip area.
NOTE: The brow lowering you see in nose wrinkler is not directly caused by the levator labii superioris alaeque nasi (LLSAN) muscle. Rather, it is caused by the brow lowering muscles often paired with nose wrinkler: depressor supercilii and procerus. There is variable interconnectivity between these muscles and the LLSAN.
AU10 – upper lip raiser
levator labii superioris
AU10 ACTION:Upper lip raiser lifts top lip (in a more lateral manner than nose wrinkler).
AU18 ACTION:Lip pucker draws the lip corners medially.
NOTE 1: Incisivus labii superioris and incisivus labii inferioris are considered accessory muscles to orbicularis oris.
NOTE 2: Lip pucker typically co-activates vertical lip tightener (as seen in this example). Learn more about vertical lip tightener under the “ORBICULARIS ORIS ACTIONS” section below.
AU20 – lip stretcher
risorius
AU20 ACTION:Lip stretcher draws the lip corners laterally, stretching the lips.
NOTE1: Not to be confused with mouth stretch. Mouth stretch refers to forced (not due to relaxation) jaw lowering (see “JAW ACTIONS” section below).
NOTE2: Risorius is one of the most variable facial muscles in humans. Depending on the study, it has been reported missing in anywhere from 1-94% of research subjects. Risorius is narrow and difficult to locate; so it is possible that this discrepancy in statistics is partly inflated due to methodological study errors. For more on anatomical variation, book a studio lecture on facial muscle diversity.
LOWER LIP & CHIN AREA
FACS name
muscle name
expression reference
AU16 – lower lip depressor
depressor labii inferioris
AU17 – chin raiser
mentalis
ORBICULARIS ORIS ACTIONS
FACS name
muscle name
expression reference
AU8 – lips toward each other
orbicularis oris
AU22 – lip funneler
orbicularis oris (peripheral portion)
AU23 – lip tightener
partially #notFACS
See “NOTE” below.
orbicularis oris (marginal portion)
horizontal type
vertical type
NOTE: This 2-type distinction is a deviation from official FACS. Only “horizontal type” qualifies as lip tightener in original FACS. I have chosen to divide lip tightener into two types, because the lips tighten in distinct manners. The muscle behind both movements, orbicularis oris, possesses rich variation in fiber directionality; such directional variation yields more potential actions for orbicularis oris than have thus far been documented. The distinction of horizontal vs. vertical lip tightening proves especially useful when breaking down speech. For speech references, visit the Viseme Cheat Sheet.
AU24 – lip presser
orbicularis oris (marginal portion)
Read about lip presser asymmetries in speech here: M-B-P Bilabial Visemes. (Useful for those working on lipsync and automated speech solutions.)
AU28 – lips suck
orbicularis oris (marginal and peripheral portions)
NOTE 1: AU17 – chin raiser appears during the in-between steps. I cannot perform this action without assistance from AU17 during the transition to the final pose. Mentalis appearance during lips suck is likely the case for many others as well.
NOTE 2: Jaw drop is almost always required for lips suck.
JAW ACTIONS
FACS name
muscle name
expression reference
AU26 – jaw drop
masseter, relaxed temporalis and relaxed internal pterygoid
AU27 – mouth stretch
pterygoids, digastric
AD29 – jaw thrust
pterygoids (& some masseter)
NOTE: “AD” refers to “action descriptor.” An action descriptor is basically a less fleshed out action unit (AU). ADs differ in that they function more as event descriptors.
AD30 – jaw sideways
pterygoids & temporalis
AU31 – jaw clencher
temporalis, masseter, pterygoids
MISCELLANEOUS ACTIONS
FACS name
muscle name
expression reference
AD19 – tongue show
it depends**
NOTE: “AD” refers to “action descriptor.” An action descriptor is basically a less fleshed out action unit (AU). ADs differ in that they function more as event descriptors. In this case, AD19 – tongue show, simply means the tongue is protruding in a notable way beyond typical protrusion for speech, eating, breathing, etc. For a deep dive into tongue actions and tongue-related muscles, book a mini course on tongue movements and tongue anatomy.
AU21 – neck tightener
platysma
NOTE: You may see some AU20 – lip stretcher in the AU21 – neck tightener example and vice versa. This concurrence is due to a close relationship between the risorius and platysma muscles.
AU25 – lips part
it depends**
NOTE: In FACS, AU25 – lips part, refers to the state of the lips being parted. This parting can be caused by any action that separates the lips – e.g. relaxation of mentalis, relaxation of orbicularis oris, contraction of other muscles, etc.