Injectable · lower face
Masseter reduction
Botulinum toxin into the chewing muscle, to narrow the lower face. One of the few things on this list where the cause can be self-diagnosed in about five seconds.
Not medical advice. This page explains what a procedure is and what is known about it. It is not a recommendation, and it says nothing about whether you are a candidate for anything. Only a licensed provider who has examined you can tell you that.
What it maps to in LooksRatio
- Jaw-to-cheekbone widthhow wide the jaw is relative to the cheekbones
The five-second test
Put your fingers on the back corner of your jaw, just in front of and below the ear, and clench. If a hard lump pushes out into your fingers, that is masseter, and it is muscle rather than bone. A large one widens the lower face, and it is the specific situation this treatment is for. If nothing much moves, the width is bone and this page is not your answer.
Enlarged masseter goes with clenching, grinding and heavy gum chewing, and it is common enough that it is worth checking before anybody contemplates jaw surgery.
What it is
Botulinum toxin injected into the masseter on each side. It is the same toxin used in the forehead, in larger doses, placed in a muscle rather than under skin. The treatment is well established for masseter hypertrophy and for bruxism, and in many countries this specific use is off-label, which is worth knowing and is not the same as it being unstudied.
How it works
The toxin blocks the signal from nerve to muscle. A muscle that cannot contract fully atrophies from disuse, and the visible narrowing follows the atrophy rather than the injection: it appears over four to eight weeks and peaks around three months. Ultrasound studies measure real reductions in muscle thickness, and repeat treatments produce more sustained narrowing than a single one.
Recovery
There is none to speak of. A few injections, some soreness, and normal activity immediately. The effect wears off over four to six months as the nerve terminals regenerate, and the muscle rebuilds unless the treatment is repeated.
Risks and what actually goes wrong
Chewing fatigue with hard food for a few weeks. Asymmetry if the dosing is uneven between sides. Paradoxical bulging of the anterior masseter, where the untreated part of the muscle pushes forward on clenching. Spread to the risorius or zygomaticus major producing a temporarily lopsided smile, which is the one that reliably alarms people and which resolves on its own.
Long-term, heavy, repeated dosing has been associated with reduced bone in the jaw angle in some reports, on the ordinary principle that bone follows load. It is a reason for a conservative dose and a real interval between treatments rather than a reason to avoid it.
Lower-commitment alternatives
If clenching is the cause, treating the clenching is upstream of all of this: a night guard from a dentist, and whatever is driving the habit. That does not shrink an already enlarged muscle quickly, but it stops feeding it.
What LooksRatio assumes
This is listed as a lower-commitment alternative and credited with reaching roughly 35% of what jaw contouring surgery does for this measurement, and only in the specific case where the width is muscle. The app measures width from a photograph and cannot tell muscle from bone, which is what the clench test at the top of this page is for. It is also not permanent: stopping returns the muscle to where it started.