Key takeaways
- A stiff or uneven smile after masseter Botox comes from toxin reaching a nearby smile muscle, and it tends to ease as the effect fades.
- Timeline: In a 10-person study, smile changes peaked at week 4, and nobody still had them at week 24.
- A bulge that appears only when clenching is a separate issue; in one case report, a small top-up injection improved it within 1 week and corrected it by week 2.
- Get care right away if you have trouble swallowing, speaking, or breathing, or you see double, even weeks after the injection.
Yes, an awkward or lopsided smile after jaw (masseter) Botox usually fades as the toxin wears off, and the surrounding-muscle weakness behind it can last up to about 12 weeks. It happens when some of the toxin drifts forward from the chewing muscle into a thin smile muscle near the mouth corner. A bulge that pops out only when you clench is a different problem, and it's worth a separate look.
Why Does My Smile Look Stiff After Jaw Botox?
Why Does My Smile Look Stiff After Jaw Botox?
Your masseter is the thick chewing muscle at the angle of your jaw. Just in front of it runs the risorius, a thin strap of muscle that pulls the mouth corner outward when you smile. If some toxin spreads forward from the masseter and weakens the risorius, your mouth corner won't lift as far. If it reaches one side more than the other, your smile can look crooked.
Risorius: a thin facial muscle that runs from the side of the cheek to the corner of the mouth and helps pull it sideways when you smile.
Why Does My Smile Look Stiff After Jaw Botox?
Unintended weakness of nearby muscles is an uncommon side effect of botulinum toxin, showing up in fewer than 10% of treatments overall. It's the same drug doing the same job, just in a muscle you didn't mean to relax.
How Common Is It After Masseter Botox?
How Common Is It After Masseter Botox?
The numbers vary a lot by study, mostly because the dose and injection method differ. Here's what three groups of patients showed:
- 10 women followed for 24 weeks: At week 4, 6 said their smile felt limited and 2 had a visibly uneven smile. They received a fairly high dose on each side, and the group was very small.
- 80 patients reviewed over one year: 2 (2.5%) developed smile asymmetry.
- 239 patients treated with a deep, fan-shaped technique: No persistent smile asymmetry was found over an average follow-up of about 4.9 months.
In other words, a stiff smile isn't rare in every series, but it's usually temporary. Keep in mind that how your face responds depends on your muscle size, your dose, and where the injections went. Results differ from person to person.
Stiff Smile, Clenching Bulge, or Chewing Fatigue?
Stiff Smile, Clenching Bulge, or Chewing Fatigue?
The first thing to notice is when the change shows up. A stiff smile points to the small muscle near your mouth. A bulge that pops out only when you clench points to part of the masseter itself. Getting tired quickly while chewing tough food simply means the toxin is working where it was placed.
| Stiff or uneven smile | Bulge when clenching | Chewing fatigue | |
|---|---|---|---|
| When you notice it | Smiling or talking | Biting down hard | Chewing tough food |
| Likely cause | Toxin reached the risorius | Part of the masseter stayed active | Masseter is weakened |
| Over time | Fades with the toxin | May fade or need a top-up | Gone by about week 12 in one study |
| What to record | Smiling photos | Clenching photos | Which foods, how long |
The bulge is often called paradoxical masseteric bulging. A broad tendon inside the masseter can act like a wall, so toxin relaxes the fibers on one side of it while the fibers on the other side keep working. When you clench, those active fibers bunch up and stick out. In the 239-patient series, 2 people (0.8%) had a brief local bulge that went away on its own. In one case report, the doctor injected a few extra units into the bulging fibers, and it improved within 1 week and was corrected by week 2.
How Many Weeks Until It Wears Off?
How Many Weeks Until It Wears Off?
Botulinum toxin starts weakening muscle within 2 to 4 days, peaks at around 10 days, and wears off as nerves form new connections after roughly 3 months. Unintended weakness in nearby muscles can last up to 12 weeks. In the 10-person study, the number who said their smile felt limited went from 2 at week 2 to 6 at week 4, dropped to 3 at week 12, and reached 0 by week 24.
How Many Weeks Until It Wears Off?
Jaw slimming follows its own, slower clock. Lower-face width changed only a little at 2 weeks, was greatest at 12 weeks, and partly came back by 24 weeks. So don't judge your result at week 2 or 3. Photos taken at the same angle a few weeks apart tell you far more than the mirror on a single day.
What's Normal, and What Needs Care Right Away?
What's Normal, and What Needs Care Right Away?
A small bruise at the injection site, mild swelling on the day of treatment, and tired jaw muscles when you chew are expected. In the 10-person study, chewing fatigue was most common at weeks 2 to 4, and nobody still had it at week 12. If your smile looks off but you can close your lips, drink, and speak normally, it's reasonable to keep taking photos and watch.
The symptoms below are different. The FDA warns that the effect of botulinum toxin can spread away from the injection site, and these problems can appear hours, days, or weeks after an injection:
- Trouble swallowing, speaking, or breathing
- Loss of strength or muscle weakness all over the body
- Double vision, blurred vision, or drooping eyelids
- Hoarseness or a change in your voice, or trouble saying words clearly
- Loss of bladder control
If you notice any of these, don't wait it out. Call your doctor or get medical help right away. Swallowing and breathing problems can be life-threatening.
What Should You Track Before Your Next Jaw Botox?
The most useful details for planning your next treatment are the number of units per side and how deep they went. Ask the clinic that treated you for the product name, the units on each side, and the injection date. Then take one smiling photo and one clenching photo at week 2 and week 4, in the same light. Those two shots show which muscle changed.
If you're in Seoul and want STON Clinic to take a look, include those three details and the day your smile first felt off in your first message. Whether to repeat the same dose or change the depth is decided after looking at those records alongside an exam.
If this raised a question about your own skin
Ask a questionReferences
- Symptoms of toxin spread and when they can appear — U.S. FDA, 2024 — U.S. Food and Drug Administration
- When botulinum toxin starts and wears off, and nearby muscle weakness — DermNet — DermNet NZ
- 10 people followed for 24 weeks after masseter Botox — An Bras Dermatol, 2014 — PubMed Central
- Side effects in 80 masseter Botox patients — Int J Dermatol, 2025 — PubMed Central
- Why a clenching bulge happens and how it's corrected — Int J Womens Dermatol, 2021 — PubMed Central
- 239 masseter Botox patients — Aesthetic Plast Surg, 2026 — PubMed Central
- Muscle thickness and tendon shape in bulging masseters — J Cosmet Dermatol, 2026 — PubMed Central
- Ultrasound-guided vs. standard masseter injection in 20 people — Toxins, 2020 — PubMed Central
Frequently asked questions
Q. What if my smile still looks stiff after 12 weeks?
A. If there's no improvement after 12 weeks, it's worth getting re-examined. Nearby-muscle weakness from botulinum toxin typically lasts up to 12 weeks, and in a 10-person study nobody still had smile changes at week 24. Bring your injection date and the photos you've taken.
Q. Does a bulge when I clench mean the Botox didn't work?
A. Not necessarily. It may mean only part of the masseter relaxed. In an 80-patient review, 2 people (2.5%) developed this bulge and another 2 developed smile asymmetry. A small top-up into the bulging fibers is one approach that's been used, so take a clenching photo and have it checked.
Q. Will jaw Botox also help with teeth grinding?
A. In a small study, it helped but didn't last. All 8 people who ground their teeth improved, and 7 stayed improved for more than 3 months. By week 24, only 1 still had that benefit.
Q. Can I get jaw Botox again if my smile was affected last time?
A. Once the smile change has fully resolved, a past episode doesn't automatically rule out another session. In the 10-person study, 80% said they'd repeat the treatment despite side effects. Tell your provider what happened and how many units you had, so they can plan where to inject.
Q. Does ultrasound-guided injection lower the risk of a bulge?
A. It may help, but the evidence is still small. In a study of 20 Korean volunteers, each with one side injected by ultrasound and the other without, the only bulge appeared on a non-ultrasound side, and it resolved after a compensating injection. Another analysis found that muscles that bulged were thicker to begin with.
Jangju Kim Senior Director
JANGJU KIM
Dr. Jangju Kim is a clinic director at STON Clinic, LOTTE HOTEL in Myeongdong.
Career / Education
- 현) 스톤클리닉 명동 롯데호텔 원장
- 경희대학교 의과대학 졸업
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