Medically reviewed by Dr. Hootan Zandifar, MD, FACS — double board-certified facial plastic surgeon, Beverly Hills & Santa Monica · 2026-09-04
Quick answer: Masseter Botox slims the jaw by relaxing the masseter — the thick chewing muscle at the back of the jaw. As the muscle softens with repeated treatment, the lower face can narrow into a slimmer, less square shape. Results build over weeks, last a few months, and require maintenance. It can also ease jaw clenching.
Why the masseter creates a square jaw
The masseter is a powerful chewing muscle. In some people — often those who clench or grind — it becomes enlarged, widening the lower face into a square or heavy look. This is muscle, not bone, which is why it can respond to Botox.
How the treatment slims the jaw
Botox placed into the masseter reduces its activity, and over repeated sessions the muscle gradually shrinks from reduced use, narrowing the lower face. The slimming builds over several weeks rather than appearing overnight.
It also helps clenching and grinding
Because it relaxes the same muscle, masseter Botox often relieves jaw tension, clenching, and grinding (bruxism) — a functional bonus alongside the slimming effect.
What it can’t do
If your wide jaw is from bone rather than muscle, Botox won’t reshape it — that’s a surgical question. An exam determines whether your jaw width is muscular, skeletal, or both.
Key points
- Relaxes the masseter chewing muscle to narrow the lower face.
- Slimming builds over weeks; lasts a few months; needs maintenance.
- Often relieves clenching and grinding.
- Won’t change a jaw that’s wide from bone.
Frequently asked questions
How long does masseter Botox last?
Typically a few months; repeated sessions can prolong the slimming effect as the muscle reduces.
Is it permanent?
No — it requires maintenance, though the muscle can stay smaller with consistent treatment.
Will it affect chewing?
It reduces excess muscle activity while preserving normal function in appropriate dosing, reviewed at your visit.
Is my wide jaw muscle or bone?
An in-person exam determines this — Botox helps muscular width, not skeletal width.
Related on this site: Botox · chin filler vs. chin implant · buccal fat removal.
Talk to a Beverly Hills specialist
To find out whether your jaw width is muscular and would respond to masseter Botox, Dr. Zandifar sees patients in Beverly Hills and Santa Monica and reviews your anatomy in person before recommending anything. Request a consultation.
Dr. Hootan Zandifar, MD, FACS, is a double board-certified facial plastic surgeon and otolaryngologist practicing in Beverly Hills and Santa Monica. Educational information only, not medical advice.
