A wide or square shaped lower face in many patients is due to enlarged jaw (masseter) muscle. The masseter muscle is the main chewing muscle—that has increased in size from chronic overactivity. Masseter hypertrophy is therefore a condition due to muscle physiology. With repeated clenching and grinding, the muscle grows larger just like any other muscle trained over time.
Masseter hypertrophy is an increase in the size of the masseter muscles, typically presenting as a fullness at the angle of the jaw. It may be purely aesthetic, or associated with symptoms such as jaw tightness, fatigue with chewing, facial pain, or features of temporomandibular disorders (TMD).
Common contributing factors include:
A 2025 study found bruxism is associated with a larger masseter cross-sectional area, suggesting a structural link between parafunctional activity and muscle size.
Clinically, I find masseter hypertrophy is most useful to categorise in two ways—because treatment and expectations differ:
Most often:
Muscle responds to repeated load by adapting. With more frequent, strong contractions (i.e. clenching or grinding), the jaw muscles increase in muscle fibre size and functional capacity. The result is a more prominent masseter contour at rest and/or during clench
Treatment options for enlarged jaw muscles include:
Botulinum toxin type injections temporarily reduces muscle contraction strength. Over weeks, reduced functional load can lead to a decrease in muscle thickness and volume and a softer lower-face contour.
A typical consultation and treatment pathway at The Skin Longevity Clinic:
We confirm the fullness is truly masseter (not parotid gland enlargement, salivary issues, dental pathology, or other causes of swelling near the jaw angle). This differential diagnosis is emphasised in clinical reviews and case discussions.
Treatment is tailored to your muscle bulk and facial biomechanics, with a conservative, staged approach when appropriate.
You may notice mild soreness or chewing fatigue early on. Effects build gradually over weeks; contour refinement typically becomes clearer by the 1–3 month period.
Potential side effects include:
Because masseter reduction is not just “jaw slimming.” It’s a balance of:
At The Skin Longevity Clinic, the approach is:
Enlarged jaw muscles or masseter hypertrophy, which often occurs due to bruxism. Bruxism has been linked to reduced sleep quality and longer term cardiovascular events. Treatment of masseter hypertrophy and bruxism involves accurate diagnosis, addressing the behaviour of clenching with neuromodulators and/or mouth guards and treating any trigger for the behaviour.