Botulinum Toxin for the Lower Face and Neck: Beyond the Upper-Face Basics

By the time you are comfortable softening a glabella, the upper face can feel almost forgiving: the muscles are broad, the margin for error is generous, and a slightly heavy result usually reads as "rested" rather than "wrong". The lower face and neck are a different discipline. Here the muscles are small, superficial and functional, they interdigitate with one another, and they do the daily work of smiling, speaking, chewing and swallowing. A dose that would be trivial in the frontalis can, a few millimetres off target, produce a crooked smile, an incompetent lip or, at the neck, difficulty swallowing. This is toxin work where anatomy, conservative dosing and patient selection carry far more weight than any published unit figure.

Masseter: jawline slimming, bruxism and the case for restraint

Masseter injection is probably the most requested lower-face indication, serving two overlapping goals: slimming a wide or square lower face, and easing the pain and tooth wear of bruxism and masseter hypertrophy. The evidence base is now reasonably robust. A controlled phase 2b trial of onabotulinumtoxinA for masseter muscle prominence reported investigator-rated improvement in around nine in ten treated patients by day 90, with a favourable safety profile at the doses studied [1]. Injection is intramuscular, into the bulk of the muscle low on the mandibular angle, staying below and behind a line from the tragus to the mouth corner to avoid the risorius and zygomaticus fibres that would weaken the smile.

Two cautions deserve emphasis. First, placing toxin too high or too superficially risks catching the smile elevators and producing an asymmetric or effortful grin. Second, more is not better over time: a triple-blinded randomised trial found that repeated injections reduced not only muscle thickness but also bite strength and masticatory performance, with function not fully recovered at six months [2]. For a purely aesthetic patient, a single well-placed treatment is often enough, and repeat courses warrant an honest conversation about chewing function.

The gummy smile

Excessive gingival display on smiling is frequently driven by an overactive lip-elevator complex, and small doses of toxin into the levator labii superioris alaeque nasi can meaningfully lower the upper lip's excursion. A widely cited series treating this muscle reported high satisfaction and a low complication rate, and noted that asymmetric smiles could be balanced with correspondingly asymmetric dosing [3]. The technique is unforgiving: the injection points sit high in the nasolabial fold region, and overtreatment or diffusion into the levator labii superioris or zygomaticus can flatten the whole upper lip, blunt the smile or lengthen the philtrum. Start low, review at two weeks, and top up rather than chase an immediate result.

Downturned mouth corners and the mentalis

A persistently sad or tired lower face often reflects hyperactivity of the depressor anguli oris (DAO), which pulls the oral commissures down. Relaxing the DAO lets the elevators lift the corners, but the muscle is narrow and sits close to the depressor labii inferioris, so a stray injection weakens the lower lip and disturbs speech and symmetry. Anatomical work targeting the DAO recommends injecting laterally and low, near the mandibular border away from the depressor labii, using conservative volumes [4]. The mentalis, treated for a dimpled or "peau d'orange" chin, is approached deep and in the midline; too high a placement here can drop the lower lip. DAO and mentalis are often addressed together because their activity is linked.

Perioral lines and the "lip flip"

Fine radial lip lines and a lip that disappears on smiling can be softened with tiny aliquots into the orbicularis oris just above the vermilion border, the so-called lip flip producing subtle eversion of the upper lip. This is the definition of microdosing: a few units spread across several points, never encroaching on the commissures. Overtreatment produces the classic complications of an incompetent mouth, difficulty with straws, sibilants and drinking, and trouble pronouncing plosive sounds. Musicians who play wind instruments and anyone reliant on precise oral competence should be counselled or excluded.

Platysmal bands and the Nefertiti lift

At the neck, vertical platysmal bands can be softened by injecting small aliquots along each visible band, while treatment of the platysma's downward pull along the mandibular border, the Nefertiti lift, can sharpen a soft jawline. A prospective study of botulinum toxin for neck rejuvenation found significant improvement in banding and high satisfaction, but was clear that results depend on selecting patients with muscular banding and retained skin elasticity rather than true skin laxity or heavy jowling, which toxin cannot correct [5]. An anatomical review of platysma injection stresses shallow, precisely placed points and modest per-point dosing to avoid diffusion into the deeper strap muscles, where dysphagia, dysphonia and neck weakness become real risks [6].

Dosing philosophy and patient selection

Across all of these indications the same principles recur. Exact unit figures vary by product, formulation and guidance, so treat published numbers as orientation rather than a recipe, and dose to the individual muscle you can see and palpate. Undertreat deliberately, review at two weeks, and add rather than subtract, because you cannot remove toxin once placed. Screen carefully: pre-existing asymmetry, prior surgery, occupational demands on speech or wind-playing, and unrealistic expectations all change the risk calculus. Photograph at rest and in animation, and document baseline asymmetries before you inject.

Because the safe corridors here are measured in millimetres and depth, the lower face and neck are best learnt with a mentor beside you, watching your needle placement on a real patient rather than a diagram.

References

Liew S, Jones D, Dayan S, et al. A Controlled Phase 2b Trial to Assess the Efficacy and Safety of a Single Intervention of OnabotulinumtoxinA for Treating Masseter Muscle Prominence. Aesthetic Surgery Journal. 2025.
Nobre BBS, Rezende L, Câmara-Souza MB, et al. Exploring botulinum toxin's impact on masseter hypertrophy: a randomized, triple-blinded clinical trial. Scientific Reports. 2024.
Sucupira E, Abramovitz A. A simplified method for smile enhancement: botulinum toxin injection for gummy smile. Plastic and Reconstructive Surgery. 2012.
Yi KH, Lee JH, Hu HW, et al. Novel anatomical proposal for botulinum neurotoxin injection targeting depressor anguli oris for treating drooping mouth corner. Anatomy & Cell Biology. 2023.
Jabbour SF, Kechichian EG, Awaida CJ, Tomb RR, Nasr MW. Botulinum Toxin for Neck Rejuvenation: Assessing Efficacy and Redefining Patient Selection. Plastic and Reconstructive Surgery. 2017.
Yi KH, Lee JH, Lee K, Hu HW, Lee HJ, Kim HJ. Anatomical Proposal for Botulinum Neurotoxin Injection Targeting the Platysma Muscle for Treating Platysmal Band and Jawline Lifting: A Review. Toxins (Basel). 2022.

This article is educational and does not replace formal, supervised clinical training or local regulatory requirements.