DAO Botox is an injection of botulinum toxin into the depressor anguli oris muscle, a small fan-shaped muscle that pulls the corners of your mouth downward. By weakening this muscle, the opposing muscles that lift the mouth corners gain a relative advantage, creating a subtle upward shift that softens a downturned or “sad” resting expression. Doses are small, typically a few units per side, and the treatment has become one of the more popular lower-face applications of botulinum toxin, though it demands more anatomical precision than the forehead or crow’s feet injections most people associate with Botox.
What the DAO Muscle Actually Does
The depressor anguli oris originates along the lower jawbone as a broad, fan-shaped sheet and narrows as its fibers converge toward the corner of the mouth, inserting into a fibrous hub called the modiolus. A cadaver study measured the muscle’s origin along the mandible at roughly 39 mm wide, with its fibers passing in front of the first molar on their way to the modiolus, which sits about 10 mm to the side of and 10 mm below the mouth corner.1PubMed. Topographic and Neural Anatomy of the Depressor Anguli Oris Muscle and Implications for Treatment of Synkinetic Facial Paralysis When this muscle contracts, it tugs the mouth corner downward and slightly outward, the motion you make when frowning or expressing sadness or disgust.
Your mouth corners sit at the intersection of several muscles pulling in different directions. The zygomaticus major lifts the corner up and out when you smile. The levator anguli oris pulls it straight up. The DAO pulls it down. At rest, the balance between these opposing forces determines whether your mouth corners sit in a neutral position, curve slightly upward, or droop. As you age, the DAO can become relatively dominant because the overlying skin and fat lose volume and elasticity, allowing gravity and the downward pull to win out. That’s why many people develop a progressively downturned mouth over time, and it’s the reason DAO Botox exists as a treatment.
How the Injection Creates a Lift
Botulinum toxin blocks the chemical signal that tells a muscle to contract. When injected into the DAO, it weakens the muscle’s ability to pull the mouth corner down. The upward-pulling muscles on the other side of that tug-of-war, the zygomaticus major and levator anguli oris, are left unopposed, and they gently elevate the corner into a more neutral or slightly upturned position.2Aesthetic Surgery Journal Open Forum. Creating Lift in the Lower Face With Botulinum Toxin A Treatment The change is not dramatic. You won’t suddenly look like you’re smiling. The effect is more like erasing a frown you didn’t know you had.
A prospective study that tracked patients before and 30 days after DAO treatment found an average increase in commissural height (the vertical position of the mouth corner) of about 5%, which was statistically significant. Clinicians and patients both rated the oral commissure as improved on a severity scale after treatment.3PubMed. Understanding clinical meaningfulness when targeting the depressor anguli oris muscle (DAO) with neuromodulators That said, the same study found something worth knowing: when patients were asked whether the overall change to their appearance was meaningful using a broader aesthetic improvement scale, the scores did not reach significance. In other words, the mouth corners moved measurably, but many patients didn’t perceive the result as a dramatic transformation. This is important context for managing expectations.
Dosing and Technique
DAO Botox uses very low doses compared to forehead or glabellar treatments. Published protocols describe about 2.5 units per side for onabotulinumtoxinA (Botox), incobotulinumtoxinA (Xeomin), or prabotulinumtoxinA (Jeuveau), or roughly 5 units per side for abobotulinumtoxinA (Dysport), which uses a different unit scale.4Aesthetic Surgery Journal Open Forum. Creating Lift in the Lower Face With Botulinum Toxin A Treatment One technique uses a three-point injection pattern in the upper portion of the DAO at 1.5 units per site.5Dermatologic Surgery. A Novel 3-Point Injection Technique for OnabotulinumtoxinA in the Upper Depressor Anguli Oris The total per side is modest, but because the area is anatomically crowded, the placement matters far more than the dose.
An anatomical study proposed optimized injection sites based on external facial landmarks, aiming to standardize the procedure and reduce both the number of injection points and the total dose needed while minimizing complications.6PubMed Central. Novel anatomical proposal for botulinum neurotoxin injection targeting depressor anguli oris for treating drooping mouth corner Some practitioners now use ultrasound guidance to visualize the muscle in real time, which can help distinguish the DAO from its neighbors.7SpringerLink / Aesthetic Plastic Surgery. Ultrasound-Guided “Cross Injection” Technique for Mouth Corner Lift with Botulinum Toxin Type A Most experienced injectors, though, rely on palpation and anatomical landmarks rather than imaging.
Why the Lower Face Is Trickier Than the Upper Face
For years, botulinum toxin in the lower face was treated cautiously because the muscles there are smaller, closer together, and more functionally interconnected than those in the forehead region. The DAO sits right next to the depressor labii inferioris (DLI), a deeper muscle that pulls the lower lip downward. Their fibers overlap medially, and in a cadaver study of 40 half-faces, about 45% of specimens showed a deep layer of the DAO passing underneath the DLI, sometimes connecting to yet another small muscle called the incisivus labii inferioris.8Journal of Craniofacial Surgery. An Anatomic Study of the Medial Fibers of Depressor Anguli Oris Muscle Passing Deep to the Depressor Labii Inferioris Muscle This overlap means that hitting the wrong muscle by even a few millimeters can produce noticeable asymmetry.
On the lateral side, the DAO borders the risorius, the zygomaticus major, and the platysma. If the toxin diffuses too far laterally, it weakens muscles you want to keep working, and the lifting effect disappears. The margin for error is slim in every direction, which is why injectors who are not confident they can consistently locate the DAO may reasonably choose to skip it altogether. A Nefertiti lift, for instance, focuses on the platysma along the jawline and the mentalis under the chin and can create lower-face improvement without directly treating the DAO.9Aesthetic Surgery Journal Open Forum. Creating Lift in the Lower Face With Botulinum Toxin A Treatment
Complications and What to Watch For
The most common complication of DAO Botox is inadvertent weakening of the depressor labii inferioris, the muscle right next door. When that happens, the lower lip on the treated side drops or inverts, especially during speech or animation, creating a lopsided look that can be more bothersome than the original concern. The anatomical overview in one clinical guide describes this as the single most frequent issue with DAO injections and recommends avoiding injection too medially, where the two muscles overlap.10Aesthetic Surgery Journal Open Forum. Creating Lift in the Lower Face With Botulinum Toxin A Treatment
A practical tip that shows up in the clinical literature: after injecting the DAO at the mandibular border, gentle lateral massage right away can push the toxin away from the DLI and toward the DAO’s bulk. If DLI weakness does occur, one suggested remedy is injecting a tiny amount of toxin (half a unit to one unit) intradermally into the orbicularis oris on the opposite side to even out the lower lip. That’s a fix for asymmetry, not a treatment, and it underscores how forgiving the upper face is by comparison and how unforgiving the lower face can be.
Bruising at the injection site is possible, as with any injection, but tends to be minor. Functional problems with eating, drinking through a straw, or articulating certain sounds are rare at the low doses used for cosmetic DAO treatment, but they have been reported anecdotally. Because the effects of botulinum toxin are temporary, lasting roughly three to four months, any complication will resolve on its own as the toxin wears off.
Combining DAO Botox with Fillers
DAO Botox addresses the muscular component of downturned mouth corners, but much of what creates the sad or tired look in the lower face is volume loss. Marionette lines, the creases that run from the mouth corners to the jawline, deepen as fat pads descend and skin loses elasticity. Botox alone doesn’t fill those grooves. That’s where dermal fillers come in.
A study using both hyaluronic acid filler and incobotulinumtoxinA together for downturned mouth corners found that the combination produced satisfying results, correcting the droop, smoothing oral commissures, and softening marionette lines in patients who felt they looked perpetually sad.11PubMed. Nonsurgical correction of drooping mouth corners using monophasic hyaluronic acid and incobotulinumtoxinA A case report on multimodal lower-face rejuvenation similarly combined botulinum toxin, hyaluronic acid filler, and deoxycholic acid (for jowl fat reduction) in a single visit to treat marionette lines and jowling together.12PubMed Central. Lower Face Rejuvenation with Injections: Botox, Juvederm, and Kybella for Marionette Lines and Jowls
The rationale is straightforward. Botox relaxes the muscle pulling down; filler restores the volume that gravity and aging have depleted. Neither fully addresses the problem alone, and for patients with moderate to severe marionette lines, the combination tends to produce noticeably better results than either treatment in isolation. Some practitioners inject the botulinum toxin first and wait a couple of weeks for it to take full effect before adding filler, so they can assess how much structural support is still needed.
Who Gets the Most Benefit
If you have a naturally strong DAO and relatively mild volume loss, meaning the downturned corners are mostly a muscular issue rather than a sagging-and-hollowing issue, you’re likely to see the best results from DAO Botox as a standalone treatment. This profile is more common in younger patients, roughly in their thirties to mid-forties, who notice a persistent frown at rest but don’t yet have deep marionette folds.
Older patients or those with significant lower-face volume loss may find the improvement from DAO Botox alone underwhelming, and this likely explains the mixed satisfaction scores in the prospective study noted earlier, where measurable lift did not always translate to perceived improvement.13PubMed. Understanding clinical meaningfulness when targeting the depressor anguli oris muscle (DAO) with neuromodulators For these patients, combination therapy makes more sense. Expecting DAO Botox alone to transform a heavily lined lower face is setting up for disappointment.
Facial asymmetry can also be a factor. Some people have a DAO that pulls harder on one side than the other, producing a unilateral droop. Treating just the stronger side, or using a slightly higher dose there, can restore symmetry without making the whole lower face look treated.
DAO Botox for Facial Palsy
Beyond cosmetic use, DAO Botox has a well-established role in managing facial nerve paralysis. When one side of the face is paralyzed, the unaffected side’s muscles pull without opposition, creating pronounced asymmetry. The smile becomes crooked, the mouth corner on the healthy side rides much higher, and the overall expression looks distorted. Injecting botulinum toxin into the DAO on the healthy side weakens it deliberately, bringing the two sides closer to balance.14PubMed Central. Botulinum Toxin Type A to Improve Facial Symmetry in Facial Palsy: A Practical Guideline and Clinical Experience
This application requires a careful hand for different reasons than cosmetic injection. The goal isn’t to create maximum lift but to match the weak side, so the dose has to be titrated conservatively. Over-injecting the healthy side can make both sides look paralyzed, which patients understandably find more distressing than the original asymmetry. Synkinesis, a condition where facial nerves regenerate abnormally after injury and cause involuntary movements (your eye twitches when you try to smile, for example), is another scenario where DAO injections are used therapeutically to break unwanted movement patterns.
Differences Between Botulinum Toxin Products
Three botulinum toxin type A products dominate the market for this procedure: onabotulinumtoxinA (Botox), abobotulinumtoxinA (Dysport), and incobotulinumtoxinA (Xeomin). Their units are not interchangeable. A laboratory analysis found that the actual neurotoxin content per vial varied substantially: about 0.90 nanograms of active 150-kDa toxin per 100-unit vial of Botox, 0.40 ng per 100-unit vial of Xeomin, and 2.69 ng per 500-unit vial of Dysport.15PubMed Central. AbobotulinumtoxinA (Dysport®), OnabotulinumtoxinA (Botox®), and IncobotulinumtoxinA (Xeomin®) Neurotoxin Content and Potential Implications for Duration of Response in Patients At FDA-approved doses for upper-limb spasticity, Dysport delivered a greater total amount of active neurotoxin than the others, which may partly explain clinical observations that Dysport tends to have a wider diffusion radius and can spread further from the injection point.
For DAO treatment specifically, the clinical conversion ratio described in published protocols is roughly 1:1 between Botox, Xeomin, and Jeuveau, and about 1:2 for Dysport (so 2.5 units of Botox per side becomes 5 units of Dysport per side). In practice, your injector’s familiarity with a particular product matters at least as much as the biochemical differences, because experience with diffusion patterns and onset timing for a given product affects placement decisions.
The Emotional Expression Question
One concern that comes up frequently, especially among people considering lower-face Botox for the first time, is whether weakening the DAO will interfere with your ability to express emotions naturally. The DAO is active when you frown, express displeasure, or convey sadness. If it’s weakened, can you still make those expressions?
At cosmetic doses, the answer is generally yes. The goal is partial weakening, not paralysis. You still have some DAO function, and other muscles (the platysma, the mentalis) also contribute to downward facial expressions. The change is subtle enough that most people around you won’t realize you’ve had anything done; they’ll just perceive your resting face as slightly more pleasant or approachable.
Interestingly, some researchers have explored the flip side of this question: if lifting the mouth corners changes not just how others perceive you but how you actually feel. The facial feedback hypothesis suggests that facial expressions can influence your emotional state, not just reflect it. One theoretical paper noted that DAO treatment, by facilitating a mouth configuration associated with positive affect, could hypothetically have a mood-enhancing effect, but stressed that no controlled studies have tested this specifically.16PubMed Central. A Psychological Guide to Lower Face Botulinum Toxin Injections: Baseline Emotional Functions of Facial Expressions It’s a fascinating idea, but right now it’s speculation rather than evidence.
A Uniquely Human Muscle
The DAO muscle has an unusual evolutionary story. A comparative anatomy study examined facial muscles across humans, great apes, and other primates and found that the DAO, as a distinct muscle originating from the mandible and inserting into the mouth corner, appears to be unique to humans. In great apes, the equivalent region is covered by a single continuous muscle sheet running from the upper jaw to the lower jaw margin without a separate mandibular attachment. Other primates showed an even simpler arrangement, with just a single band descending from the upper jaw toward the mouth corner.17PubMed Central. Anatomical Evidence for a Uniquely Human Depressor Anguli Oris and a Novel Helplessness Signaling Hypothesis
The researchers proposed that the DAO may have evolved as part of a uniquely human signaling system. Pulling the mouth corners downward is central to the expression of sadness and helplessness, emotions that in humans serve a social function: they signal vulnerability and recruit care from others. In the study, all 61 human specimens had a clearly distinct DAO with two identifiable bellies, while none of the non-human primates had anything comparable. If this hypothesis holds, the muscle that cosmetic patients want to quiet down may have been shaped by millions of years of social evolution to do exactly what it does: broadcast distress to the people around you.