There is a particular kind of vanity that hides inside a complaint about drooling. A patient will mention, almost as an aside, that her pillow is damp in the morning, and then — in the same breath, more carefully — that she has never liked how heavy her jaw looks from below, in photographs taken slightly downward. These sound like two different problems. Clinically, they can be the same gland.
In 1759, Étienne de Silhouette was France's finance minister for a humiliating eight months, remembered afterward mostly for the austerity he imposed and, more unfairly, for the cheap paper-cut portraits that came to bear his name — a single unbroken line standing in for an entire likeness, no shading, no color, nothing but the edge of a profile traced from a shadow. The silhouette was mocked in its own century as the portrait of someone too poor for a real one. But the form also carried a genuine belief, borrowed from the physiognomists fashionable in the same decades: that the line of a jaw held more information than people wanted to admit about the person underneath it. Cut the profile correctly and you had, supposedly, the truth of a face. Cut it wrong — a jaw a few millimeters too heavy, a chin dropped too low — and you had simply gotten someone's likeness incorrect.
I think about that a great deal when a patient sits down and asks me to soften her jawline with an injection into the submandibular gland. It is, in its own quiet way, the same problem the silhouette-cutter had: reduce a three-dimensional, moving, individually variable structure to a single reliable line, and then trust that line completely. The difference is that a bad silhouette embarrasses no one but the sitter's vanity. A needle that misses its mark in the floor of the mouth can do considerably more.
What the Injection Is Actually For
The submandibular gland sits just beneath the body of the mandible, roughly where a heavy or "full" under-jaw contour is often blamed on fat or muscle it doesn't actually have. Botulinum toxin injected into the gland works the way it works everywhere else — by blocking acetylcholine release, in this case at the parasympathetic nerve endings that drive glandular secretion — and the effect is twofold. Resting salivary output drops, which is the actual indication in patients with chronic drooling or sialorrhea, and the gland itself undergoes a degree of volumetric atrophy with repeated treatment, which is the reason it has migrated into aesthetic practice as a way to soften the lower face without touching the masseter at all. Hong (2023) describes the analogous parotid protocol — 20 to 30 units, injected more superficially than the masseter, chosen specifically because high-dose treatment of both major salivary glands simultaneously risks a genuinely unpleasant degree of dry mouth, since the submandibular gland is responsible for most resting salivary flow. It is not the same procedure as masseter reduction for a squarer jaw; it is solving a different, lower, softer part of the same silhouette.
The Cadaver's Map
Because the gland cannot be seen from the outside, clinicians who inject it without imaging rely on surface landmarks — and the most-cited version of that landmark comes from a cadaveric study by Lee et al. (2010), who dissected 34 submandibular glands across 20 specimens to work out exactly where the gland sits relative to bone. Their answer: draw a line from the angle of the mandible to the gnathion — the lowest point of the chin — and the gland's safest injection zone falls between 20% and 35% of the way along that line, measured from the angle, at a depth of roughly 2.0 cm and about 1.5 cm below the inferior border of the mandible. It is, in effect, a formula for the same problem the silhouette-cutter solved with scissors: here is where the line runs, memorize its proportions, and you no longer need to see the thing itself to find it.
Does the Formula Actually Land on the Gland?
This is the part the marketing rarely gets into, and it happens to be the part I have spent a fair amount of my own research life on. So et al. (2017) tested exactly this question on six fresh-frozen cadavers, injecting colored dye into the parotid and submandibular glands on each side — one side guided by surface landmarks alone, the other under real-time ultrasound — and then dissecting every specimen to see where the dye actually ended up. For the parotid gland, a large, forgiving target sitting in the hollow behind the jaw angle, landmark guidance was reasonably accurate: 79.17% correct placement versus 95.83% with ultrasound, a gap that didn't reach statistical significance. For the submandibular gland — the smaller, more mobile structure this article is actually about — landmark guidance placed the toxin correctly only 50.00% of the time, against 91.67% with ultrasound, a difference that was statistically significant (p = .025). Pooled across both glands, blind injection hit its target 69.4% of the time versus 94.4% with imaging (p = .006). Put plainly: for the parotid gland, a steady hand and a good grasp of anatomy will usually get the job done. For the submandibular gland, roughly one injection in two misses when guided by landmarks alone, ending up instead in the mylohyoid muscle or the surrounding subcutaneous tissue.
When the Miss Isn't Trivial
A case report published earlier this year makes the stakes concrete. Yang and Yi (2026) describe a healthy 37-year-old woman who received a purely cosmetic, landmark-guided injection of incobotulinumtoxinA — 20 units per side, 40 units total — into both submandibular glands, with no ultrasound involved. Within a day she noticed an abnormal sensation in her throat; within two, she had frank dysphagia, choking on liquids, and nasal regurgitation. The authors attribute it to some combination of local diffusion of the toxin into adjacent pharyngeal muscles and an excessive reduction in resting saliva, which together impaired her ability to form a bolus and trigger a normal swallow. Recovery required three months of structured swallowing rehabilitation — chin-tuck maneuvers, the Shaker exercise, the Masako maneuver, neuromuscular electrical stimulation — before she reached a near-normal Functional Oral Intake Scale score, and a full five months before her swallowing returned entirely to baseline. Nothing about her case was unusual or negligent by the standard of how this injection is still commonly performed. That is precisely the point.
The Honest Answer
None of this means landmark-guided injection should be abandoned outright, particularly for the parotid gland, where the anatomy is forgiving enough that the accuracy gap barely matters. But for the submandibular gland specifically — the one most patients are actually asking about when they mention a heavy under-jaw line — the data argue for ultrasound guidance as something closer to a standard of care than an optional upgrade. If you're considering this treatment, it is a fair and specific question to ask your injector: are you visualizing the gland directly, or are you finding it the way an eighteenth-century silhouette-cutter found a jawline — by trusting a formula, in the dark, and hoping the proportions hold for this particular face. Most of the time they do. The 2026 case report exists because, once in a while, they don't, and the cost of that miss is paid in a part of the body considerably more consequential than a likeness.
References
Hong, S. O. (2023). Cosmetic treatment using botulinum toxin in the oral and maxillofacial area: A narrative review of esthetic techniques. Toxins, 15(2), 82. https://doi.org/10.3390/toxins15020082
Lee, J. H., Lee, B. N., Kwon, S. O., Chung, R. H., & Han, S. H. (2010). Anatomical localization of submandibular gland for botulinum toxin injection. Surgical and Radiologic Anatomy, 32(10), 945–949. https://doi.org/10.1007/s00276-010-0647-z
So, J. I., Song, D. H., Park, J. H., Choi, E., Yoon, J. Y., Yoo, Y., & Chung, M. E. (2017). Accuracy of ultrasound-guided and non-ultrasound-guided botulinum toxin injection into cadaver salivary glands. Annals of Rehabilitation Medicine, 41(1), 51–57. https://doi.org/10.5535/arm.2017.41.1.51
Yang, S., & Yi, Y. G. (2026). Dysphagia after cosmetic submandibular gland botulinum neurotoxin type A injection: A case report. Healthcare, 14(2), 235. https://doi.org/10.3390/healthcare14020235
