How to mew correctly
The technique is simple. The claims around it are not supported.
Read this first
Tongue posture does not remodel adult facial bone. The orthodontic work the practice borrows from concerns growing children, where jaw development is genuinely still in progress, and generalising it to adults is the error the whole category rests on. What mewing can plausibly affect in an adult is muscle tone and habitual posture, which change how a jaw reads without changing the angle underneath it.
Mewing is a specific posture rather than an exercise: the whole tongue rests flat against the roof of the mouth, including the back third, the lips stay closed, the teeth touch lightly without clenching, and breathing happens through the nose. Most people who say they are mewing are holding only the tip of the tongue up, which is ordinary tongue position and not the practice. Done correctly it is a resting posture held most of the day rather than a set of repetitions. What it will not do is change your gonial angle, lift your midface or widen your palate as an adult; those claims come from paediatric orthodontics and do not transfer. What it may do is improve nasal breathing habits and resting jaw posture, both of which are worth having on their own terms.
What actually works
Get the back third of the tongue up
Say the letter N and hold where the tongue lands, then bring the rest of it flat to the palate behind that. If only the tip is touching, you are not doing the thing the practice describes.
Close the lips, touch the teeth lightly
Lips sealed, teeth in contact without pressure, jaw relaxed. Clenching is a different behaviour with its own problems and is not part of this.
Breathe through your nose
The posture is unmaintainable with the mouth open, so nasal breathing is a prerequisite rather than a benefit. If you cannot breathe through your nose comfortably, that is the thing to address first, and it is a medical question.
Hold it at rest, not as reps
It is a default position, not an exercise. Sets and repetitions are a misunderstanding that comes from the fitness framing, and pushing hard against the palate is how people end up with jaw pain.
Measure it, so you know whether anything moved
How defined is my jawline?Jaw-to-cheekbone width ratio, scored with the gonial angle.
Questions
How long does mewing take to work?
For the bone changes usually claimed, it does not, at any duration. For resting posture and nasal breathing habits, weeks. Any timeline offered for jaw remodelling in an adult is describing something that has not been shown to happen.
Can mewing hurt you?
Pushing hard against the palate can cause jaw and tooth discomfort, and a few case reports describe dental movement from sustained force. The correct version is a light resting posture, not pressure, which is also the version nobody demonstrates in a short video.
Does mewing work for adults at all?
Not for what it is sold for. The orthodontic literature behind it concerns children whose jaws are still growing. In adults the plausible effects are on muscle tone and habitual posture — real, but not what the before-and-after images claim.