The muscle grows; it's in the wrong place. Press behind the corner of your jaw and clench. The slab that bulges out is the masseter, and like any muscle it hypertrophies under daily load ¹. But it sits behind the visible jawline. The sharp chin-to-ear border is fat, bone, and skin, three things chewing doesn't touch. Growing the masseter pushes that back corner outward, which reads as a wider, squarer face.

The people with thick masseters have wider, squarer lower faces. That's the consistent finding from ultrasound studies of jaw-muscle thickness ², ³. Whether an adult can deliberately train that muscle and have anyone notice a cosmetic change is untested — the one published training study ran on ten still-growing teenagers for four weeks and never measured how the face looked ⁴. The viral before-and-afters almost always overlap with real weight loss in the same window, which sharpens any jaw on its own.

What actually defines a lower face, roughly in order of effect: lose body fat. The fat under the chin tracks your total, and a few kilos off visibly sharpens the jaw within months. Fix a forward head posture; a neutral neck recovers the jaw-to-neck angle for free. Filler along the bone line is immediate and lasts about a year. If you've already over-built the masseter, botox shrinks it back over six to eight weeks ⁵, the same treatment Korean clinics built a specialty around.

If you're going to use a chewing device anyway, use the harm-floor version. Moderate chewing is fine; nobody's jaw broke over a piece of gum. The damage comes from the maximum-resistance, twice-a-day, push-through-soreness routine the gadgets are sold for.