How to Relax the Depressor Anguli Oris Muscle

The depressor anguli oris, a thin fan-shaped muscle just below each corner of the mouth, is the muscle responsible for pulling your mouth corners downward. Relaxing it typically involves one of three approaches: botulinum toxin injections to temporarily weaken the muscle, biofeedback training to teach conscious control over involuntary contraction, or surgical removal of part of the muscle in more severe cases. Which approach makes sense depends on whether you are dealing with cosmetic concerns like marionette lines or a medical condition like post-paralysis facial synkinesis.

What the DAO Does and Why It Matters

The depressor anguli oris (DAO) sits just beneath the skin on either side of your chin, running from the lower jawbone up to the corner of the mouth. Its job is straightforward: it pulls the mouth corners down and slightly outward. This is the muscle that shapes a frown, and it plays a role in expressions of sadness, displeasure, and concentration.¹ One recent evolutionary study even proposed that the human DAO has a uniquely derived architecture that may have been recruited into an expressive facial signal associated with helplessness during infancy, suggesting this muscle has deep roots in how we communicate vulnerability.²

When the DAO is overactive or chronically tense, the mouth corners droop even at rest, giving a person a perpetually sad, tired, or angry look.³ Over time, this repeated downward pull also deepens marionette lines, the creases that run from the mouth corners down toward the jawline. These folds are considered one of the hallmark signs of facial aging, and the DAO’s contraction is the main muscular force driving them.⁴

Botulinum Toxin Injections

The most common clinical approach to relaxing the DAO is injecting a small dose of botulinum toxin (commonly known by brand names like Botox, Dysport, or Xeomin) directly into the muscle. The toxin blocks the chemical signal that tells the muscle to contract, weakening it for roughly three to four months. The goal is not to paralyze the muscle entirely but to dial down its pull enough that the mouth corners sit in a more neutral or slightly upturned position at rest.

A prospective study using incobotulinumtoxinA (Xeomin) combined with hyaluronic acid filler found that the approach produced satisfactory results in patients whose drooping mouth corners gave them a saddened appearance.⁵ In a different clinical context, weakening the DAO with botulinum toxin in patients recovering from facial paralysis improved smile symmetry by about 2 mm of excursion and shifted perceived emotion from negative to positive in a significant proportion of patients.⁶

The effect is temporary, which is both the advantage and the limitation. If you do not like the result or experience a side effect, it wears off. But if you want to maintain the relaxation, you need to return for repeat treatments every few months.

Why DAO Injections Are Trickier Than They Sound

On the surface, injecting one small muscle sounds simple. In practice, the DAO sits in a crowded neighborhood. Its inner border overlaps with the depressor labii inferioris (the muscle that pulls your lower lip down), and its outer edge lies right next to the risorius, the zygomaticus major, and the platysma.⁷ If the toxin spreads into any of these neighboring muscles, you get unintended effects. Weakening the depressor labii inferioris, for instance, can cause asymmetric lower lip movement, making it difficult to bare your lower teeth on the affected side or creating a lopsided smile.

A published case report described exactly this scenario: botulinum toxin intended for one area diffused into the DAO on one side, paralyzing the adjacent depressor labii inferioris and causing visible asymmetry of the lower lip.⁸ This is why researchers have worked to standardize injection guidelines that reduce both the dose and the number of injection points, aiming to maximize the intended relaxation while keeping the toxin from wandering into the wrong muscle.⁷

Ultrasound imaging has started to play a role here. A prospective study measured the depth from skin to the DAO muscle and found it averaged roughly 5 to 8.5 mm depending on the location along the muscle, with the lateral border sitting deeper than the medial edge.⁹ Knowing these depths before injecting helps practitioners place the needle more precisely. Ultrasound has also been validated as a way to clearly visualize and measure several facial muscles, including the DAO.¹⁰

Combining Botulinum Toxin with Dermal Fillers

In cosmetic practice, botulinum toxin injections into the DAO are frequently combined with hyaluronic acid fillers rather than used alone. The logic is that the toxin handles the muscular component, reducing the downward pull, while the filler adds volume to the creases and commissures that have already formed. Relaxing the muscle alone does not erase a deep marionette line that has been etched into the skin over years; it just stops the line from getting worse.

Research supports the combined approach. One study using both monophasic hyaluronic acid and incobotulinumtoxinA corrected drooping mouth corners, deep oral commissures, and marionette lines in a single treatment session, with median filler volumes of about 0.2 to 0.25 mL per side for the mouth corners themselves and a total mean neurotoxin dose of roughly 26.5 units.⁵ The simultaneous application of both substances appears to produce better outcomes than either one alone.¹¹ A case study even explored adding synthetic deoxycholic acid (a fat-dissolving agent used for double chins) to the mix for lower face rejuvenation, treating jowls alongside the mouth corners in one office visit.¹²

If you are considering this combination route, the filler typically lasts longer than the toxin. Hyaluronic acid fillers hold their shape for six months to a year or more, while the neurotoxin wears off in three to four months. That means you might need a toxin touch-up between filler appointments to maintain the full effect.

Biofeedback Training for Conscious Relaxation

Not all DAO relaxation requires needles. For people recovering from facial nerve palsy, a common problem is synkinesis: involuntary contraction of one muscle when you try to move a different one. Your DAO might fire every time you blink or purse your lips, creating an unwanted downward tug at the mouth corner. In these cases, biofeedback training can teach the brain to decouple those movements.

The setup uses surface electromyography (EMG) sensors placed on the skin over the muscles of interest. The patient sees a real-time display of their muscle activity. When they perform an intended movement, such as pursing the lips, the screen also shows whether unrelated muscles like the DAO are firing at the same time. The patient then practices the intended movement while consciously trying to keep the unintended muscle activity as low as possible, guided by the visual feedback.¹³ In one training protocol, patients practiced for three hours per day, working to control a target movement without triggering synkinetic activity in other facial muscles.

The results are measurable. A study of biofeedback training in patients with post-paralytic facial synkinesis found a significant decrease in EMG amplitudes on both the synkinetic side and the unaffected side after completing the training program, indicating improved voluntary muscle relaxation.¹⁴ The improvement on both sides is telling: it suggests the training does not just suppress one rogue muscle but teaches broader neuromuscular control over facial expressions.

Biofeedback is not a quick fix. It demands consistent practice over weeks or months, and it works best for people whose DAO overactivity stems from misfiring nerve signals rather than structural muscle tension or aging-related changes. But for synkinesis patients, it offers something injections cannot: the possibility of retraining the nervous system rather than temporarily silencing the muscle.

Surgical Options for Persistent Cases

When botulinum toxin is not enough or when the problem is severe and structural, surgery becomes an option. The most common procedure is a DAO myectomy, meaning removal of a portion of the muscle itself. This is most frequently performed in patients with facial nerve paralysis who have developed contractures or chronic synkinesis that resists other treatments.¹⁵

Myectomy does come with challenges. Because the DAO’s borders blend into neighboring muscles, it can be difficult during surgery to know exactly where the DAO ends and the next muscle begins. This means the recurrence rate is relatively high if not enough muscle tissue is removed. Some surgeons recommend resecting 2.5 to 3 cm of muscle length to reduce the likelihood of the muscle growing back functionally. There is also an opposite risk: removing too much can create a visible depression or hollow in the chin area. In patients with chronic facial nerve paralysis, the DAO and its neighbor the depressor labii inferioris can thicken by more than 20 percent, making it even harder to judge the right amount of tissue to remove.¹⁶

To address the potential for post-surgical hollowing, some practitioners combine the myectomy with placement of a pedicled buccal fat pad flap, essentially repositioning nearby fat tissue to fill the space left by the removed muscle and maintain facial symmetry. This combined approach is particularly useful for chronic paralysis cases where both the excess muscle pull and the resulting contour deformity need correction.

Cosmetic Versus Medical Contexts

The reason for wanting to relax the DAO shapes the entire treatment approach, and it is worth understanding the distinction. In the cosmetic setting, you are typically dealing with a normally functioning muscle that is simply a bit too strong for your aesthetic preference, or whose effects have accumulated over decades of facial expression, deepening marionette folds. The treatments are lower-stakes: small doses of botulinum toxin, possibly combined with filler, aimed at softening the resting expression. If the result is imperfect, it fades.

In the medical setting, DAO overactivity is often part of a larger problem. After facial nerve paralysis from Bell’s palsy, surgery, or another cause, the nerve sometimes regenerates imperfectly. Nerve fibers that originally controlled one muscle can accidentally reattach to a different muscle, producing synkinesis. The DAO is a common culprit: it contracts involuntarily during movements like eye closure or smiling, dragging the mouth corner down at inappropriate times and distorting expressions. In a study of 20 patients with unilateral post-paralysis facial palsy and marked DAO synkinesis, weakening the overactive DAO improved smile symmetry significantly and shifted observer perception of the affected side from negative to positive emotion in nearly twice as many faces.⁶

For synkinesis patients, treatment is usually staged. Botulinum toxin serves as a first-line trial to confirm that weakening the DAO actually improves function and appearance. If it does, the patient can continue with repeat injections or opt for a more permanent solution like myectomy. Biofeedback training often runs in parallel, addressing the broader pattern of misfiring rather than just the DAO in isolation.

What You Can Do at Home

If you are reading this because you have noticed your mouth corners turning downward with age and want to try something before seeking a clinic visit, the honest answer is that home approaches are limited in what they can achieve for this particular muscle. The DAO is not a muscle you can easily isolate with facial exercises the way you might stretch your jaw or relax your forehead. Consciously relaxing it requires first being aware that it is contracting, which most people are not. Habitual tension in the lower face often goes unnoticed because it feels like your “neutral” expression.

That said, a few things may help at the margins. Becoming aware of jaw clenching and lower face tension throughout the day is a reasonable starting point, since the DAO often co-contracts with the mentalis (the chin muscle) during moments of concentration or stress. When you catch yourself tensing your chin or pressing your lips together, consciously letting the lower face go slack can gradually reduce baseline tension. Some people find that gently placing a fingertip at each mouth corner and noticing whether the corners tend to pull downward gives them enough sensory feedback to begin recognizing and releasing the contraction.

Massage of the lower face, while not studied specifically for DAO relaxation in otherwise healthy people, follows the general principle that manual pressure can temporarily reduce muscle tone. Gentle circular motions along the jawline from chin to ear, spending extra time at the area just below each mouth corner, may provide modest relief for tension-related tightness. This will not produce anything close to the effect of botulinum toxin, but it costs nothing and carries no risk.

The DAO and Your Smile Type

An interesting detail from the research is that DAO thickness is not the same in everyone, and it appears to correlate with the kind of smile a person naturally produces. A sonographic study measuring several facial muscles found that people with a “full denture” smile, where both upper and lower teeth are visible, tended to have a thicker DAO and mentalis compared to people with a “canine” smile, where mostly the upper teeth show.¹⁷ In other words, the balance of power between the muscles that lift the mouth corners and the muscles that pull them down helps determine what your smile looks like.

This matters practically because a thicker, more powerful DAO may require a slightly higher dose of botulinum toxin to achieve the same degree of relaxation, and it helps explain why the same injection protocol can produce different results in different people. It also underscores that the DAO is not purely a “frowning” muscle. It participates in complex expressions including certain types of smiles, and completely eliminating its function would not necessarily improve your appearance. The goal of any relaxation treatment is to modulate its pull, not abolish it, preserving the muscle’s contribution to natural-looking facial movement while reducing the aspects that make you look unhappy at rest.