Masseter Botox in San Francisco: Does It Slim the Jaw?
By Roy Kim, MD, board-certified plastic surgeon | Updated September 2026
Overview
Yes, for most patients whose jaw width comes from the masseter muscle. Botox shrinks the masseter muscle, which gets smaller over the following weeks, resulting in a more narrow face
- It treats muscle bulk, not bone or fat.
- It can also reduce clenching and grinding, aka bruxism
- The change is gradual and lasts as long as you keep up treatments.
1. How does masseter Botox slim the jawline?
The masseter is the muscle at the angle of your jaw that closes your bite. You can feel it and see it when you clench your jaw.
If Botox is injected into the masseter muscle, it shrinks, and the lower face looks more narrow, especially from the front.
People who clench or grind often have a larger masseter, and that can make the lower face look square.
Masseter reduction is one of the most common aesthetic treatments in Korea, where a narrower lower face is a popular goal. This technique has spread worldwide.
2. Is my wide jaw from muscle, fat, or bone?
Lower face width can come from the masseter, the jawbone, or fat in the cheeks and along the jaw. Botox only changes the muscle, so it helps when the muscle makes up a large part of the width.
If the width is bone, the option is surgery, such as mandibular angle reduction. If it is fat, options include buccal fat removal and liposuction of the jaw and neck.
Many faces have more than one cause. In that case, Botox narrows only the part of the width that comes from muscle.
3. How long does it take to see a slimmer jaw?
Slimming is gradual. The visible change comes from the muscle shrinking, and you start to see a difference at 2 weeks, with the full effect at 3-6 weeks.
You won't see a difference on the day of treatment, so plan ahead if you're timing it for an event.
4. How long does masseter Botox last?
Results last about 4-6 months. The muscle slowly regains its strength and width, so you will need repeat treatments to keep the slimmer contour.
If you stop, the muscle returns to its original size and your face goes back to where it started. It doesn't end up wider than before.
5. What are the risks of masseter Botox?
Masseter Botox is generally safe. The side effects I watch for are an uneven smile, a bulge when you clench, weaker chewing, and hollowing below the cheekbone. All of them wear off as the Botox does.
- Uneven smile. The risorius, a small muscle that pulls the corner of the mouth outward, sits in front of the masseter. If Botox spreads into it, your smile can look uneven until it wears off. This is very rare, since the masseter muscle is so far away from this muscle.
- Bulge on clenching. If part of the muscle isn't treated, that part can bulge when you bite down. A touch-up to that area usually corrects it.
- Hollowing. In a thin face or a face with loose skin, a smaller masseter can make the area below the cheekbone look hollow or make loose skin along the jaw more visible.
To find out whether masseter Botox fits your face, call my San Francisco or Alameda office at 415-362-1846.
6. What happens at the treatment visit?
The injections take a few minutes. I ask you to clench your teeth so I can feel the borders of the muscle, then inject several points in the masseter.
Most patients describe a quick pinch. There's no downtime, and you can go back to work afterward.
The dose is set by the size and strength of the masseter muscle. If you have any asymmetric muscle, you may need an asymmetric amount of Botox units injected into each side.
7. Does masseter Botox help with clenching, grinding, or TMJ pain?
For many patients, yes. Weakening the masseter muscles reduce how hard you can clench, which can ease grinding along with the jaw soreness and headaches that come with it.
If the pain comes from the joint itself, such as a disc problem or arthritis, Botox may ease muscle tension but won't treat the joint. That needs an evaluation by your dentist or an oral surgeon.
Comparison: Masseter Botox vs. Jaw Reduction Surgery
Both narrow the lower face. They treat different structures.
Myths About Masseter Botox
Myth: Masseter Botox works right away. It takes several weeks, because the effect comes from the muscle getting smaller.
Myth: Masseter Botox lifts jowls. Jowls come from tissue that has descended and from loose skin, and reducing masseter width and size does little to the jowls.
Jowls are best treated surgically, with a deep plane facelift, an SMAS facelift, or a mini lift. [LINK: Deep Plane Facelift for Jowls]
Myth: Stopping treatment makes your face wider. The muscle returns to its original size, not larger.
Frequently Asked Questions
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Not yet. Botox is FDA approved for other uses, and treating the masseter is an off-label use. Recently, in September 2026, the FDA is looking closely into Botox use in the masseter muscle, and should release a final decision shortly.
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That is set by the size and strength of your muscle, and the two sides often differ. A typical range is 20-50 units per side, depending on the size and strength of your masseter muscles.
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No. Other neuromodulators work the same way. Letybo is my preferred alternative to Botox, but technically, any neuromodulator is a possibility.
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You can still eat normally.
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Cosmetic jaw slimming is not.
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Yes. It is often done at the same visit as Botox for forehead lines or frown lines.
Summary
Masseter Botox narrows the lower face by shrinking the chewing muscle at the angle of the jaw.
It works on muscle, not on bone or fat.
Slimming builds over several weeks and lasts for about 4-6 months.
Masseter Botox can also reduce clenching and grinding.
Schedule a Consultation
To schedule a consultation, call 415-362-1846 or email info@drkim.com. I'll talk with you about your goals and examine your face and jaw.
Roy Kim, MD, board-certified plastic surgeon
450 Sutter Street, Suite 1440, San Francisco, CA 94108
1403 Park Street, Alameda, CA 94501