What changes when masseter Botox is repeated

Some patients stand at the mirror pressing both sides of the jaw with their hands, saying that this part sticks out and makes the face look wide. Where the hand sits is the first clue. A patient pressing the hollow below the ear and a patient pressing the corner of the jawbone lead to different conversations.

Of the patients who ask about masseter Botox, roughly half actually have a masseter as the cause. For the rest, the bone angle is naturally wide, or the lower face has dropped and made the jawline heavy. Inject without separating those and a few months later you hear that nothing changed.

Why I check first whether it bulges when you clench

The examination is done by hand. I place my fingers below the ear over the molar area and ask you to clench hard and release. If the muscle rises and falls under my fingers, the masseter is the thick part. If nothing moves however hard you clench and all I feel is something solid, that is bone.

Then I add one more check. I ask you to lie down and look at the same area again. If the jawline sharpens lying down and the heaviness you were bothered by eases, part of what looks square is actually sagging. In that case reducing the muscle will not give you the line you want.

What Botox cannot do when the bone is the angular part

Patients show me family photos and say their mother has the same jaw. That is usually a wide bone angle. Reduce the muscle and the outline of the bone stays exactly where it was.

Even so, these patients have some muscle, so the treatment can be done. The issue is the gap between expectation and result. In this case I say in advance that it will change, but only to a degree you notice by comparing photographs. If they still want to try, we go ahead; if that is not enough for them, we do not. The same treatment is judged differently depending on what you expected when you started.

What changes at four weeks and at three months after the first round

The question I get most is when it starts to change. There is an order. First, within a few days, chewing takes less effort. The muscle actually thinning comes after that. From around four weeks it starts to show in photographs, and the greatest reduction sits between six weeks and three months.

Then it comes back gradually. A muscle thins when it is not used and thickens when it is used again; that is its nature. The next round is usually considered between three and six months. That interval differs from person to person, and it shortens if the clenching habit is unchanged.

How the masseter changes over repeated rounds

From the second round the questions change. Either "does it keep getting smaller if I keep going" or "can I stop now". A recent study addressed exactly this, and I quote it often in consultation.

In a triple blinded randomised controlled trial published in Scientific Reports in 2024 (14:14561), a second round was given into the masseter and the patients were assessed at six months. The muscle was thinner than after a single round, and the activity measured by electromyography was lower as well. In other words, repeating gave a thinner muscle than stopping after one round.

That does not mean it keeps thinning forever. As rounds accumulate the reduction per round gets smaller, and what grows instead is how long the result holds. So from the third round I do not increase the dose. I keep the same dose and stretch the interval, looking for the interval at which it starts to thicken again.

Why the muscle got thinner while chewing performance did not change

The reason I hear most often for hesitating is chewing strength. Patients ask whether they will no longer be able to chew meat. The part of that study worth noting is exactly here. Thickness and EMG activity fell, and measured chewing performance did not change.

How should that be read? What I say in consultation is this. A muscle becoming thinner and losing the ability to break food down are different questions. The masseter is not the only muscle used in chewing, and the others take up the share that was lost.

That said, some patients genuinely do feel tired chewing something tough in the first few weeks. That is closer to unfamiliarity than to lost capacity, and it usually settles within a few weeks. For patients who love dried squid or dried meat, I start the first round at a lower dose.

Why the unit numbers differ between products

Patients treated abroad show me their records and ask for the same amount as last time. But the number cannot simply be carried across. A unit is not a measure of weight; it is an activity unit each product defines on its own terms, so the same number means a different amount when the product is different.

There is a family where 25 units per side is typical, and a family where around 60 units is written for a comparable effect. Abobotulinum units in particular do not convert one to one to other brands, so there is no simple factor to apply. Choose a clinic by price per unit and the actual amount delivered can invert. When you compare quotes, get the product name and the unit count together.

The same three things are worth writing down when you bring a record: the product name, the units used per side, and the date. I read that and decide whether to go the same as last time or adjust.

Hollow cheeks and awkwardness when smiling

Occasionally a patient comes back saying their cheeks look hollow. When the muscle shrinks, the bulk that covered it shrinks too, and for someone whose facial fat was never generous that reads as gaunt. The jaw is slimmer and the overall impression is tired.

Some also say their smile feels odd. Muscles used in facial expression run above and in front of the masseter. If the injection sits too far forward, those can be affected. So I divide the injection behind and below the mandibular angle and keep to a line I do not cross going forward.

Hearing this, some patients ask me to use just a little. But cut the dose too far and it wears off in about a month, so they end up coming back for another round. Rather than reducing the dose, I adjust by placing it accurately.

Matching the dose when the two sides look different

Many patients come in saying one side sticks out more. Most of the time that is how they are. Chewing habitually on the dominant side develops that muscle more. So I do not put the same dose on both sides from the start; I put a little more on the thicker side.

I do not try to match them completely in the first round, though. The two sides can shrink at different speeds, so looking again at four weeks and correcting only the difference that remains is more accurate. Force the match on day one and it can flip the other way.

When I advise against masseter Botox

Some patients enquire and I tell them not to do it. First, anyone whose face is lean and whose cheeks have already hollowed. The jaw narrows and the whole face reads as older.

Second, anyone whose jawline has started to sag. When the muscle shrinks, the bulk supporting that area goes with it and the lower face can look looser. Here we settle the sagging first and look at the muscle afterwards.

Third, anyone who has trouble opening the mouth wide, or who has both clicking and pain in the jaw joint. That is not a cosmetic question, so I suggest seeing a dentist or an oral and maxillofacial surgeon first. Grinding without pain is a different conversation, but once there is pain, the order changes.

When to stretch the interval or stop

Patients often ask whether starting this means having it for life. It does not. Stop, and the muscle returns to what its usual workload supports, though getting all the way back to the starting point takes time. The more rounds someone has had, the slower that return.

After the third round I do not book by the calendar. I ask patients to wait a month longer than last time and we watch whether it thickens again. If it holds twice in a row, we stretch the interval further. Going this way, some patients settle at roughly once a year after a few years.

Sometimes I am the one who suggests stopping. That is a patient with almost no change in thickness across two consecutive rounds and no clenching habit. Continuing when there is no muscle left to reduce only costs money.

Why the result cannot be checked within a trip to Korea

Patients who fit the treatment into a travel itinerary look in the mirror the next day and are disappointed. This is not a treatment that changes anything that day. The sense that chewing takes less effort arrives within a few days, but the facial line looking different takes four weeks.

So for patients on a short trip I say two things. If you want a result photograph, take it a month from now under the same lighting rather than today, and send me a photo at around four weeks so I can check whether the two sides need correcting. For patients who cannot easily return, I do not push the first dose. When correction is difficult, too little beats too much.

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