Mewing is the claim that resting your tongue on the roof of your mouth will, over months and years, reshape your jaw and cheekbones. It has billions of views. It also has something rarer than weak evidence: none.
What the literature contains
Search PubMed for "mewing OR orthotropics" and you get 31 results. Almost all of them are commentaries by or about the technique's originator, letters in response, or unrelated papers where "mewing" refers to a cat-cry syndrome. There is no randomised trial, no cohort study and no systematic review that tests it. The closest thing is a 2025 review that screened 10,370 records and concluded, in its own words, that literature evaluating the effectiveness of mewing is extremely scarce.
That is not a technique with mixed results. It is a technique that has never been tested.
The part that should end the argument
If a resting tongue could move bone, a purpose-built appliance should do it better. That has been tested, at scale. A Cochrane review pooled 27 randomised trials with 1,251 children aged roughly 7 to 11, the years when the jaw is still growing. Children wore functional appliances daily and were compared with children who simply waited. The final skeletal outcome, the ANB angle that describes how the upper and lower jaw relate, differed by 0.02 degrees on average, with a confidence interval of minus 0.47 to plus 0.43. The single strongest appliance in the review, the Twin Block, moved it by 0.56 degrees.
Growing children, hard plastic, daily wear, and the jaw moved by a fraction of a degree. A tongue is not going to beat a Twin Block.
The advice that points the wrong way
A popular refinement says to push the tongue toward your weaker side to correct asymmetry. The entire evidence base for asymmetric tongue posture is one 2011 study of 12 people, and it found lower tongue pressure on the deviated side, which is more likely a consequence of the asymmetry than a cause of it. The advice has the arrow backwards.
What tongue posture is actually good for
None of this means the habit is worthless. Tongue on the palate, lips closed, breathing through the nose is the posture that goes with nasal breathing and a relaxed jaw, and those are real, everyday things you can feel. Symmi includes it as a habit for exactly that reason, and labels it honestly: a resting posture, not a bone remodelling program.
The jaw readings that mewing promises to change, jaw width, chin height, the mandible itself, are tagged structural in Symmi's report. They do not move with training, and the app says so on the reading. What does move is the soft tissue in front of the bone: the masseter, the fat and fluid under the chin, and the head posture that decides how sharp the edge reads. That is where the plan spends its time.
Sources
PubMed search "mewing OR orthotropics", 31 results. Seraj S.S. et al., Aesthetic Surgery Journal Open Forum 2025. Batista K.B. et al., Cochrane Database of Systematic Reviews 2018;3:CD003452.