Masseter botulinum toxin softens the jawline by reducing the strength of the chewing muscles.
Changes usually begin around 2 weeks after treatment, with a typical duration of about 4–6 months, although this varies.
Muscle size and treatment spacing can change the retreatment interval and perceived response.
➊What is masseter botulinum toxin treatment?
Botulinum toxin is injected into the masseter, the chewing muscle at the side of the jaw, to reduce its strength and size and soften the jawline.
A square jaw can reflect bone shape, but often appears angular because the chewing muscles are large and well developed.
For this muscular type, botulinum toxin reduces muscle volume to refine the jawline.
We first check how much the muscle protrudes when you clench and whether there is asymmetry.
Dose and injection sites depend on muscle size and development, so plans differ between individuals even for the same treatment.
- ✓Check muscle protrusion when clenching
- ✓Check left–right asymmetry
- ✓Plan dose by muscle size and development
- ✓Individualize injection sites
➋When do effects become noticeable?
It is normal to see little change on the treatment day.
The ingredient needs time to act on the muscle and reduce its strength.
Reduced chewing force is often noticed around 1 week, while jawline changes tend to emerge gradually after 2 weeks.
Full effects are often assessed around 4 weeks; strong or thick muscles may take longer to show a noticeable response.
➌How long does it last?
Duration varies but is often estimated at around 4–6 months.
This is somewhat longer than treatment of expression muscles. The masseter is a large, frequently used muscle, where the ingredient acts gradually and effects tend to last relatively longer.
Clenching, frequent gum chewing or heavy jaw use can make returning strength feel noticeable sooner because the muscle is used more often.
Adjusting these habits can sometimes extend the perceived benefit.
| Category | Expression-muscle botulinum toxin | Masseter botulinum toxin |
|---|---|---|
| Main target muscles | Glabellar and eye-area expression muscles | Chewing muscle (masseter) |
| Onset | Around 3–5 days | Around 1–2 weeks |
| Duration | About 3–4 months | About 4–6 months |
“Masseter treatment tends to start more slowly than expression-muscle treatment, but last longer.”
➍How many sessions are needed?
People with smaller muscles often notice satisfactory change after a single treatment.
For marked muscle development or asymmetry, I may recommend gradual adjustment over 2 or 3 sessions rather than strongly reducing force at once.
Excessive reduction at once can burden chewing function.
Temporalis treatment may also be considered, since the chewing muscle at the temples can work together with the muscles contributing to a square jaw.
| Muscle condition | Recommended approach | Retreatment interval |
|---|---|---|
| Smaller muscles | May notice change after 1 session | Around 4–6 months (varies) |
| Large muscles or asymmetry | Adjust over 2–3 sessions | Decided clinically based on progress |
“The larger or more asymmetric the muscles, the safer it is to adjust over multiple sessions rather than reduce everything at once.”
➎Precautions and adverse effects
Although widely performed, masseter botulinum toxin may cause temporary swelling, bruising or pain depending on injection location and dose.
Most settle within a few days.
Rarely, unsuitable placement or dosing can make smiling look unnatural or leave chewing strength excessively weak.
Accurately locating the muscle and matching the dose to its size help reduce these risks.
We combine muscle palpation with consultation to lower these risks.
QFrequently asked questions
No.
It takes time for the ingredient to act, so little change on the day is normal.
Chewing may feel weaker around 1 week, and jawline changes often emerge gradually after 2 weeks.
It depends on muscle size, but many notice change after the first treatment.
For large or strong muscles, gradual reduction over 2 or 3 treatments may be advised.
Heavy-use habits such as clenching or frequent gum chewing can make strength return sooner.
Adjusting those habits often extends the perceived duration.
The temporalis is a chewing muscle at the temple and may work with the masseter, so both may be addressed depending on the condition.
The decision requires assessment of muscle distribution and associated symptoms.
We assess jaw-muscle size, development and asymmetry, then plan injection sites and dose before treatment.
We then monitor progress and arrange further treatment if needed. Your own plan should be confirmed directly at consultation (individual results vary).
This does not shave down the face; it adjusts muscle strength to reveal the underlying jawline.
Reducing chewing-muscle size and strength softens the jawline; onset and duration vary with the muscle condition.
An examination at LUNN Clinic is the best way to assess your jaw muscles and expected timing.
Dr. Park Hyungkwon, Director and Dermatologist at LUNN Clinic
Under Article 56 of the Medical Service Act, we disclose possible swelling, bruising, temporary pain and, rarely, unnatural expression or reduced chewing function.
Treatment and procedure results may vary depending on the individual’s condition.
This column is intended to provide medical information.
