Masseter Botox Side Effects: What Is Normal and What Is Not

Normal in the first few days

• Tenderness or a small lump at the injection points, fading within a day or two.
• Bruising, which can take up to a week to clear. Concealer can cover it the next day.
• A mild headache on the first day.

Normal in the first weeks

• Chewing fatigue: the muscle is weaker, so tough meat or chewy food can make the jaw tire sooner. Everyday eating is not affected, and this eases as you adapt.
• A slightly different feel when you clench. This is the treatment working.

Less common effects

• Uneven smile: if the toxin reaches the muscle that pulls the corner of the mouth, one side of the smile can look different. It is temporary and settles as the effect wears off.
• Hollowing under the cheekbone: when the muscle shrinks a lot in a face with little fat, the area below the cheekbone can look sunken. A conservative dose avoids this.
• Bulging when clenching: sometimes a part of the muscle that was not treated works harder and bulges. A small top-up at the review usually evens it out.
• Uneven slimming: the two sides are rarely identical to begin with, so they may slim at different rates.

Does masseter Botox cause sagging?

This worry comes up often. Slimming the muscle does not loosen the skin, but in someone who already has laxity, a narrower lower face can make existing softness along the jaw more noticeable. That is one reason the doctor looks at skin quality and age, not just muscle size, before recommending treatment.

When to contact the clinic

• Difficulty swallowing, speaking, or breathing.
• Drooping of the eyelid or face on one side.
• Swelling, redness or pain that increases after the first two days.

These are rare, but they should be checked straight away rather than waited out.

How to lower the risk

• Choose a doctor who examines your muscle while you clench, not a fixed package dose.
• Start conservatively. It is easier to add a little at the review than to wait for too much to wear off.
• Do not massage or press the area on the day of treatment.
• Tell the doctor about pregnancy, breastfeeding, neuromuscular conditions and any medication.

Doing it safely in Seoul

At Maylin Apgujeong, a doctor sets the dose for each side after examining the muscle, offers a review once the effect has settled, and explains in writing what to expect. Consultation is in English.

The long-term questions people ask

With repeated treatment, the muscle stays smaller, which is the point of maintenance. Some studies have looked at changes in jaw bone density with repeated high-dose treatment; the findings are limited, and this is one reason doses and intervals are kept sensible rather than stacked.

If you stop, the muscle gradually regains its size and the jaw returns toward how it was.

Does the face go back to normal?

Yes. The effect is temporary. If something like an uneven smile happens, it fades as the product wears off, usually over weeks to a few months. Contact the clinic so it can be checked and, where possible, balanced.

FAQ

Plan a visit: if you have questions about side effects, send them on WhatsApp, LINE, or KakaoTalk, and a clinician will answer in English before you book.