Treatment
Jaw slimming works — if the width is muscle
A wide lower face can be muscle, bone or fat, and only one of the three responds to botulinum toxin. Feeling the masseter contract under your fingers takes ten seconds and decides whether this treatment is worth having at all.
- Appointment
- 20 to 30 minutes
- Anaesthetic
- None required; topical on request
- Onset
- Softening from week 2; visible narrowing at 6 to 12 weeks
- Duration
- Commonly 4 to 6 months, often longer with repeat treatment
- Downtime
- None. Small raised bumps settle within an hour
What it is
The masseter is the thick chewing muscle over the angle of the jaw. Like any muscle it enlarges with use, and in some people — heavy chewers, clenchers, and a good number of people simply by inheritance — it is bulky enough to widen the lower third of the face and square off the jaw.
Botulinum toxin placed into the muscle reduces how strongly it contracts. Used less, the muscle atrophies over the following weeks, and the width it was contributing decreases. The change is gradual and it is not an injection that produces a result the same week.
What is assessed
Three things widen a lower face and they look similar in a photograph. Treating the wrong one wastes months.
- Muscle — palpated while you clench. A masseter that bulges hard under the fingers is the one this treatment is for.
- Bone — a wide mandibular angle is skeletal. No injection narrows bone, and this is a surgical question if it matters to you.
- Fat — buccal and subcutaneous fullness sits forward of the muscle and is soft when the jaw is relaxed.
- Skin support — reducing masseter bulk in an older face with lax skin can, occasionally, make the cheek look emptier rather than narrower. Worth knowing beforehand.
- Asymmetry and chewing side — most people chew preferentially on one side, and the bulk differs. Doses are rarely identical left and right.
If you clench or grind your teeth, tell me. That is a medical matter rather than a cosmetic one, it belongs in the conversation, and it may mean your dentist should be involved.
What to expect, and when
- Weeks 1 to 2 — chewing feels slightly less powerful. Nothing visible yet.
- Weeks 3 to 6 — the muscle begins to reduce. Most people notice it first in photographs rather than the mirror.
- Weeks 6 to 12 — the visible narrowing. This is when the result should be judged, not before.
- Months 4 to 6 — bulk returns gradually. A second treatment at that point tends to hold longer than the first, and intervals commonly lengthen over a few cycles.
The first session is deliberately conservative. It is easy to add at review and impossible to take back, and an over-reduced masseter in a slim face is a difficult thing to wait out.
The appointment
Assessment
Photographed frontally and at three-quarters. The masseter is palpated on both sides while you clench, and its borders are marked. The parotid gland and the anterior border of the muscle are identified, because both define where injection should not go.
Consent and planning
Dose per side, the expected timeline, and the specific risks including asymmetric smile and temporary chewing fatigue are discussed before anything is drawn up.
Placement
Several points per side, deep into the lower and posterior part of the muscle, well behind the anterior border and below the level where the risorius and zygomaticus run. Doses differ between sides where the bulk differs.
Review
Seen at four to six weeks. This is when a top-up is decided, and where asymmetry is corrected.
Risks and limits
- Chewing fatigue — common and expected for the first two or three weeks, particularly with hard food.
- Asymmetric smile — from spread into the risorius or zygomaticus major if injection is placed too far forward or too superficially. Uncommon, temporary, and avoided by staying deep and posterior.
- Hollowing at the angle — over-reduction, especially in a thin face, which resolves only as the muscle returns.
- Paradoxical bulging — the upper part of the muscle can protrude on clenching if only the lower part is treated. Corrected at review.
- No effect at all — if the width was bone rather than muscle, which is precisely what the assessment is for.
Botulinum toxin is a prescription medicine, given here only after individual assessment. Duration and degree of change vary between individuals and cannot be guaranteed.
After treatment
Stay upright for four hours and avoid rubbing or massaging the area. Avoid heavy exercise, saunas and hot yoga for 24 hours. Normal chewing is fine; expect it to tire sooner for a couple of weeks. Chewing gum habitually works against the treatment, so it is worth stopping.
Come back at four to six weeks whether or not you think anything has happened — that visit is where the dose for next time is set.
Questions
Asked often
How do I know if my jaw is muscle or bone?
Clench your teeth and press the area over the angle of your jaw. If a firm mass bulges under your fingers, that is masseter. If it feels much the same clenched and relaxed, the width is more likely skeletal, and this treatment will not change it.
How long until I see my face look slimmer?
Six to twelve weeks. Chewing feels weaker within a fortnight, but the visible narrowing follows the muscle shrinking, and that is slow. Judging the result at three weeks is the commonest reason people think it has not worked.
How long does masseter treatment last?
Commonly four to six months at first. Repeat treatments tend to hold longer, and many people find the interval stretches after two or three cycles. It varies between individuals.
Will my face look sunken?
It can if the dose is too high for the amount of muscle you have, particularly in a slim or older face. That is why the first session is conservative and why the review at four to six weeks exists.
Does it help teeth grinding?
Grinding and clenching are a medical issue rather than a cosmetic one, and they should be assessed as such — often alongside your dentist. Tell me if you grind, and we will discuss it properly rather than treating it as a side benefit.
Will chewing be affected?
For the first two or three weeks, expect the jaw to tire sooner with hard or chewy food. It settles. Very few people find it interferes with normal eating.
Can I have it with other treatments?
Yes. It combines commonly with chin or jaw filler, because narrowing the width and adding projection at the front address different parts of the same complaint. Sequencing is agreed at the consultation.
Also relevant
Related treatments
Consultation
Every face is read before it is treated
A consultation establishes whether this treatment is the right one for you. Sometimes the answer is that it is not.