This post is about a variant of the zygomaticus major muscle and its effects on dimples in smiling. Before getting into the details, it is necessary to clarify which interpretation of “dimple” I am referring to.

the dimple, the dimple – it’s not that simple.

FACS-fueled confusion & linguistic disillusion 

If you’re familiar with FACS (Facial Action Coding System) terms, you will know that the “dimpler” action or AU14, is caused by the contraction of the buccinator muscle. When buccinator is activated, the corners of our lips pinch inward and push against our molar teeth, as demonstrated below:

Functionally, this action is important for chewing and keeping food in our mouths.

Outside of FACS, the word “dimple” almost always refers to an indentation of the skin (typically near the mouth or chin) caused by genetic muscle variation. For this reason, novice FACS learners often mistake any concave skin deformation as a sign of AU14; however, such assumptions are incorrect.

NOTE: I have been informed by FACS authorities that the next manual release will feature a re-naming of AU14 – one that is directly descriptive of the action itself. If my memory serves me well – it is to be called “lip corner pincher” – or something of that nature. 

what everyone else means by “dimple”

The most frequently observed facial dimples are smile-based dimples. These dimples are thought to be caused by a variation of the zygomaticus major muscle (the muscle for AU12 – lip corner puller) – a variation that involves two insertion points rather than one.

NOTE: The word “smile” has many interpretations. In this post, I will use “smile” when referring to the contraction of the zygomaticus major muscle.