Does mewing really work for a sharper jawline?
There is no clinical evidence that mewing improves the jawline in adults. Serious tongue-exercise therapy does exist, but is intended for functional problems such as abnormal swallowing, not for cosmetic purposes.
Mewing is the deliberate pressing of the tongue against the palate at rest, with the aim of achieving a sharper jawline. That idea is not entirely without basis: there are indications that a chronically low tongue posture and mouth breathing, through constant pressure on jaw and gum structures, can contribute to misaligned teeth and jaw deformities. But those indications come from limited and difficult-to-measure research. A directly measured effect of conscious tongue placement on the jawline in adults has not been demonstrated in the available studies.
The broader idea behind mewing, namely that an open-mouth posture and low chewing force cause the face to grow downward, comes from a single author who calls this 'craniofacial dystrophy'. No clinical research has tested this proposal. It is a theoretical model, not a proven mechanism.
What the research does show: tongue pressure and lip force clearly decline with age. An observational study compared healthy older adults (average age 67) with young adults (average age 22) and found significantly lower tongue and lip strength in the older group, accompanied by poorer chewing and swallowing function. This indicates that the oral muscles age, but it says nothing about whether that decline can be reversed with mewing.
There is serious therapy that targets tongue posture and the oral muscles: orofacial myofunctional therapy. That therapy, combined with physiotherapy for neck posture, improved tongue, lip and cheek function in young people with an abnormal swallowing pattern. This is, however, swallowing rehabilitation for people with a demonstrated functional problem, not a cosmetic treatment of the jawline. Do not compare it with what mewing advocates promise online.
Four sources: two on the relationship between tongue posture and jaw structure (limited evidence), one theoretical model without clinical testing, one observational study on ageing of the oral muscles, and one not further indexed study on combined tongue therapy in young people. No randomised studies on mewing as a cosmetic intervention.