Masseter Slimming: How Xeomin Can Change a Wide or Square Jawline

A wide or square-looking lower face can have several causes. In some people, one contributor is a prominent masseter—the large chewing muscle located along each side of the jaw.

When masseter muscle size is contributing to lower-face width, a wrinkle relaxer such as Xeomin may be used cosmetically to reduce activity in the muscle. Over time, reduced muscle activity can decrease masseter prominence and create a slimmer appearance through the lower face.

But masseter treatment is not appropriate for every jawline concern, and cosmetic masseter slimming should not be confused with treatment for temporomandibular joint disorders, commonly called TMJ or TMD.

What Is the Masseter Muscle?

The masseter is one of the primary muscles used for chewing.

It runs along the side of the lower face and connects the cheekbone region with the lower jaw. You can usually feel it contract by placing your fingers near the back of your jaw and clenching your teeth.

Like other muscles, the masseter varies in size from person to person.

Some people naturally have larger or more prominent masseter muscles. Repeated heavy use of the muscle may also contribute to its prominence in some individuals.

When the masseter is prominent, it can contribute to a wider or more square appearance through the lower face.

What Is Cosmetic Masseter Slimming?

Cosmetic masseter slimming uses botulinum toxin type A to temporarily reduce activity in selected portions of the masseter muscle.

Vital Glow uses Xeomin, a prescription botulinum toxin type A product.

Botulinum toxin works by reducing the nerve signals that cause a targeted muscle to contract.

For facial-expression treatments, that reduced contraction can soften movement-related wrinkles.

In the masseter, the cosmetic goal is different.

Reducing activity in a prominent muscle can gradually decrease its bulk, which may reduce lower-face width and create a softer or more tapered facial contour.

Does Masseter Treatment Actually Make the Face Slimmer?

It can when enlarged or prominent masseter muscles are an important reason the lower face appears wide.

Clinical research on botulinum toxin type A for masseter muscle prominence has found reductions in masseter thickness, prominence, lower-face width, and patient-reported concern compared with placebo.

However, the treatment changes muscle. It does not make the jawbone smaller.

That distinction is one of the most important things to understand before considering treatment.

What Determines the Shape of Your Jawline?

The appearance of the lower face can be influenced by several structures:

• Jawbone shape and width
• Masseter muscle size
• Facial fat and other soft tissue
• Skin thickness and elasticity
• Chin shape and projection
• Age-related changes in facial structure

Two people can therefore have similarly wide lower faces for completely different reasons.

If someone’s jaw appears wide primarily because of skeletal structure, reducing masseter activity will not change the underlying bone.

If the width is substantially influenced by prominent masseter muscles, muscle reduction may have a more noticeable effect.

How Can You Tell Whether Your Masseters Are Prominent?

One part of the evaluation is observing and palpating the muscle at rest and while clenching.

A prominent masseter often becomes noticeably firmer and more defined when the teeth are clenched.

But facial assessment should consider more than whether the muscle can be felt.

The provider should also evaluate overall facial proportions, symmetry, jaw structure, soft tissue, skin laxity, and the patient’s desired result.

The question is not simply:

“Can this muscle be injected?”

It is:

“Is masseter prominence actually contributing to the feature you want to change?”

How Does Xeomin Affect the Masseter Muscle?

Xeomin contains incobotulinumtoxinA, a form of botulinum toxin type A.

After injection into an appropriately selected muscle, it temporarily reduces acetylcholine-mediated signaling between the nerve and muscle.

That decreases the muscle’s ability to contract as strongly.

With cosmetic masseter treatment, the visible contour change is not necessarily immediate because the goal is not simply temporary relaxation.

As the muscle is used less forcefully over time, its prominence may gradually decrease.

How Long Does It Take to See Jaw Slimming?

The effect develops gradually.

Muscle activity begins changing before the full contour change is visible.

Research evaluating cosmetic masseter treatment commonly measures meaningful changes over the following weeks and months rather than expecting an immediate transformation.

This differs from dermal filler, where added volume can produce an immediate structural change.

With masseter slimming, the face changes as the treated muscle becomes less prominent.

Is Masseter Slimming Permanent?

No.

Botulinum toxin effects are temporary.

Over time, nerve signaling and muscle activity recover.

The cosmetic effect can therefore diminish, and some patients who want to maintain the result choose repeat treatment.

How long the visible contour change lasts varies among individuals.

Can Masseter Treatment Make a Square Face Look More V-Shaped?

Potentially, but only when masseter prominence is contributing meaningfully to the width of the lower face.

Reducing that prominence can change the relationship between the upper and lower portions of the face, sometimes creating a narrower or more tapered lower-face appearance.

It cannot completely redesign someone’s facial structure.

A naturally wide jawbone will remain wide, and other factors such as chin projection, facial fat, or skin laxity can continue to influence the overall contour.

Can Masseter Slimming Change the Jawline in an Unwanted Way?

Yes, which is one reason patient selection and conservative treatment planning matter.

Reducing masseter volume changes the soft-tissue support and contour of the lower face.

Depending on facial anatomy, excessive reduction could potentially make pre-existing skin laxity or lower-face sagging more noticeable.

A 2025 study evaluating patients after botulinum toxin treatment for masseter hypertrophy found that some developed reduced mandibular-margin definition and soft-tissue sagging after treatment.

This does not mean that everyone will develop laxity. It does mean that simply making the masseter as small as possible should not be the goal.

The desired result should fit the person’s overall facial structure.

What Are the Risks of Masseter Injections?

Possible effects of botulinum toxin injections can include:

• Injection-site pain or tenderness
• Bruising
• Swelling
• Headache
• Temporary muscle weakness
• Asymmetry
• Changes in chewing strength
• An unwanted change in facial contour

Injection placement also matters because neighboring muscles contribute to facial movement and expression.

Botulinum toxin products carry warnings about the possibility of toxin effects spreading beyond the injection site. Rare but potentially serious symptoms can include difficulty swallowing, speaking, or breathing.

A qualified healthcare provider should review relevant medical history, medications, previous botulinum toxin treatment, neuromuscular conditions, and other factors before treatment.

Is Cosmetic Masseter Slimming FDA Approved?

Botulinum toxin products have FDA-approved cosmetic indications for specific facial areas and conditions.

However, cosmetic treatment of masseter prominence is not currently among the FDA-approved cosmetic indications listed in U.S. prescribing information.

Using a medication for an indication that is not included in its FDA-approved labeling is commonly called off-label use.

Off-label does not automatically mean inappropriate or unsupported. It means the specific use is not included in the product’s FDA-approved labeling.

Research continues to evaluate botulinum toxin treatment for masseter prominence, including randomized controlled clinical trials.

Is Masseter Slimming the Same as TMJ Treatment?

No.

Cosmetic masseter slimming and treatment of temporomandibular disorders are different clinical goals.

“TMJ” technically refers to the temporomandibular joint itself. Temporomandibular disorders, or TMD, can involve the joint, chewing muscles, or related structures and can have multiple causes.

Symptoms may include:

• Jaw pain
• Joint pain
• Clicking or popping
• Limited jaw movement
• Jaw locking
• Muscle tenderness
• Headache or facial pain

Those symptoms require an appropriate evaluation because reducing activity in one muscle does not diagnose or address every possible cause of jaw pain or dysfunction.

Vital Glow’s masseter treatment is offered for cosmetic facial contouring, not as a treatment program for TMJ disorders.

What About Teeth Grinding or Jaw Clenching?

Bruxism and jaw clenching can involve increased activity of the chewing muscles, but they are not synonymous with cosmetic masseter prominence.

A person may have prominent masseters without having a painful jaw disorder, and someone with significant TMD symptoms may not have cosmetically prominent masseters.

If your primary concern is pain, jaw dysfunction, significant grinding, locking, or another functional problem, appropriate dental or medical evaluation may be more suitable than beginning with a cosmetic contouring treatment.

Masseter Slimming vs. Jawline Filler: What Is the Difference?

These treatments change the lower face in fundamentally different ways.

Masseter treatment reduces muscle activity and may gradually reduce muscle prominence.

Dermal filler adds volume and structure.

For example, filler may be used in appropriately selected patients to improve jawline definition or chin projection.

Someone with a wide lower face caused by prominent masseters has a different anatomical problem from someone who lacks jawline definition because of facial structure or volume distribution.

This is why facial balancing should begin with anatomy rather than choosing an injectable first.

Learn more about natural-looking fillers and facial balancing →

Masseter Slimming vs. Facial Weight Loss

Masseter slimming should also not be confused with losing facial fat.

Botulinum toxin does not burn fat or produce general weight loss.

It targets muscle activity.

If lower-face fullness comes primarily from fat or other soft tissue rather than masseter muscle, treating the masseter may not create the expected result.

Who May Be a Good Candidate for Cosmetic Masseter Slimming?

Potential candidates may include adults who:

• Have prominent masseter muscles contributing to lower-face width
• Want a slimmer or softer lower-face contour
• Understand that treatment affects muscle rather than bone
• Have realistic expectations about the amount of change possible
• Understand that results are temporary
• Do not have a contraindication to botulinum toxin treatment

An evaluation is particularly important when there is existing lower-face laxity, facial asymmetry, or uncertainty about whether muscle is actually responsible for the desired change.

Who Might Not Get the Result They Expect?

Someone seeking a dramatic change to skeletal jaw width may be disappointed because masseter treatment does not alter bone.

Likewise, reducing the masseter may not substantially improve a jawline concern caused primarily by:

• Chin position
• Bone structure
• Facial fat distribution
• Skin laxity
• Loss of structural support

In some faces, reducing masseter prominence could even make another concern more noticeable.

The most useful consultation therefore asks not just what treatment someone wants, but what anatomical feature is creating the appearance they want to change.

Cosmetic Masseter Slimming in Columbia, SC

Vital Glow offers cosmetic masseter treatment with Xeomin for appropriately selected patients in Columbia, South Carolina, and surrounding Midlands communities including Irmo, Lexington, Chapin, Lake Murray, and West Columbia.

Treatment begins with an evaluation of the masseter muscles and overall lower-face anatomy to determine whether muscle prominence is contributing to the desired cosmetic change.

If another anatomical factor is more important, masseter treatment may not be the appropriate approach.

Learn more about Xeomin and wrinkle relaxer treatments at Vital Glow →

Frequently Asked Questions About Masseter Slimming

Does masseter Xeomin slim your face?

It may reduce lower-face width when prominent masseter muscles are contributing to a square or wide jaw appearance. It does not change the underlying jawbone.

How quickly does masseter slimming work?

The change is gradual. Muscle activity decreases before the full cosmetic reduction in muscle prominence becomes visible, so contour changes generally develop over weeks rather than immediately.

Is masseter slimming permanent?

No. Botulinum toxin effects are temporary, and muscle activity eventually recovers. Repeat treatment may be needed to maintain the cosmetic effect.

Does masseter Xeomin treat TMJ?

Vital Glow offers masseter treatment for cosmetic facial contouring, not as treatment for temporomandibular joint disorders. Jaw pain, locking, significant clicking, or other functional symptoms should receive appropriate medical or dental evaluation.

Can masseter slimming cause sagging?

Changes in lower-face contour and soft-tissue support can occur as masseter volume decreases. Some research has documented reduced jawline definition or soft-tissue sagging in some patients after treatment. Existing skin laxity and facial anatomy should therefore be considered before treatment.

Is masseter slimming the same as jawline filler?

No. Masseter treatment reduces activity and prominence of a muscle, while dermal filler adds volume or structural definition. The appropriate approach depends on the anatomy responsible for the patient’s concern.

Is cosmetic masseter treatment off-label?

Yes. In the United States, cosmetic masseter slimming is not currently included among the FDA-approved cosmetic indications for botulinum toxin products. Clinical research nevertheless supports an effect of botulinum toxin type A on masseter prominence and lower-face width.

Medically reviewed by Candace Danbury, MSN, APRN, FNP-BC.