MID FACE Introduction With the increased demand for facial rejuvenation done by noninvasive techniques, many experienced injectors of botulinum neurotoxins (BoNTs) are now venturing below the upper face with treatments.1 At this time, however, all these treatments in the United States (US) are not Food and Drug Administration (FDA) approved and are performed in an o-label manner. As with any other part of the face, it is imperative for the treating physician to be completely knowledgeable of the dynamic balance of the levator and depressor action of the mid face mimetic musculature if successful treatments with BoNTs are to be realized. e reciprocating action of opposing mimetic muscles can prove to be a bit more complicated in anatomical morphology and function in the mid and lower face and therefore more challenging to treat than in the upper face. Specically, the muscles of the upper face are easily distinguishable from one another because of various topographic landmarks, making it easy to inject them with any BoNT. However, in the mid and lower face there is an interdependence of movement of supercial and deep mimetic muscles which also are adjacent to, and form part of, some of the muscles surrounding the mouth that function in the articulation of sounds, expression of emotions, and, or in mastication and deglutition. All adjacent mid face mimetic muscles interdigitate with each other and are invested by the supercial muscular aponeurotic system (SMAS). Many of them perform complementary and, at times, unrelated dynamic functions. e mimetic muscles of the mid and lower face have very specic functions, which are mostly centered around the mouth. ese muscles can sometimes act as agonists, sometimes as antagonists, but always in a complex, synergisticly dynamic manner. ey allow a person to smile, laugh, grimace, pucker the lips, or to make any other overt or subtle gesture with the mouth. ese complex functions permit one to hold solids, liquid, or air within the mouth without loss of contents. ey also allow one to release contents at will from the mouth either slowly or forcibly. ese muscles allow for the ne motor movements necessary to produce either subtle whispering sounds or thunderous clamor. ey also facilitate the actions of chewing, swallowing, and a myriad of other simple and complex movements that either explicitly or implicitly function in deliberate and involuntary motor movements that are so particular of an individual’s mannerisms and personality. In addition, many of these supercial and deep muscles overlie a thicker mass of so tissue as well as each other, creating an anatomy that is quite dierent from the forehead and brow. Consequently, if OnaBTX-A (OnaBTX-A) migrates beyond the targeted muscles when it is injected in the mid and lower face, unintended eects and adverse sequelae can easily occur. erefore, when treating anyone with OnaBTX-A in the lower two-thirds of the face, low doses usually are eective and higher doses are not necessarily better but instead can be rather detrimental to the dynamic balance of normal facial mimetic function.