Verdict: no evidence, for face shape in adults. Nasal breathing is a good habit for sleep and comfort. There is no study showing that taping your mouth, or switching to nose breathing, changes the shape of an adult face, and the studies people cite for it did not measure faces at all.
The whole literature fits in one sentence
A 2025 systematic review in PLOS ONE screened 120 records on mouth taping and oral closure and found 10 studies, with a combined total of 213 patients. The largest had 71 people, the smallest 9. Every one of the ten was rated poor on the Newcastle-Ottawa quality scale.
What did they measure? Sleep. Two studies showed a fall in apnoea events (8.3 to 4.7 and 12 to 7.8 per hour), both in people with mild sleep apnoea and no nasal obstruction. Three showed no change. Four of the ten warned that taping carries a serious risk of asphyxiation if the nose is blocked or there is reflux. Not one measured jaw shape, face height, symmetry or anything about appearance.
So the claim "mouth taping reshapes your face" has an evidence base of zero, and the claim "mouth taping helps you sleep" has a small, low-quality, mixed one, with a safety warning attached.
The monkey study, read properly
The face-shape claim traces back to a 1981 experiment on rhesus monkeys. Silicone plugs were sewn into the nostrils of 42 young animals for 18 months to 3 years, forcing them to breathe through the mouth. The monkeys' faces did change: longer lower faces, steeper jaw planes, wider jaw angles.
Two things get left out when this is retold. First, every monkey ended up with a different bite. One developed an underbite, one a severe open bite, one an overbite, one a double bite. The author's own conclusion was that a correlation between mouth breathing and any particular kind of malocclusion was unlikely. Second, and more important, these were growing animals. The experiment shows what forced, total nasal blockage does to a face that is still developing. It says nothing about an adult whose growth finished a decade ago.
Growing faces are the one place breathing habits plausibly matter. Even there the effect is contested: a Cochrane review of 27 trials in 1,251 children found that purpose-built orthodontic appliances worn daily changed the final jaw relationship by 0.02 degrees. A tongue or a strip of tape is not going to outperform a Twin Block.
Mouth breathing is often a habit, not a blockage
One more finding turns the sales pitch around. In a study of 116 adults measuring nasal airflow, 97% of people with a badly narrowed nasal passage breathed through the mouth, as you would expect. But among people whose airway was completely clear, about 12% still breathed through the mouth out of habit. Roughly one in eight mouth breathers has nothing wrong with their nose.
That matters because the "fix your airway, fix your face" story assumes a blockage. For many people there is none. The habit is just a habit, which is good news: it can be changed without tape, by noticing it.
What nasal breathing is actually good for
- Sleep quality, in the narrow group of mild apnoea without nasal obstruction, per the two positive studies.
- A relaxed jaw. Lips closed, tongue on the palate and nose breathing go together, and a jaw held that way at rest is more comfortable than one hanging open.
- Nothing measurable about face shape in adults. Not width, not length, not symmetry.
If you want to try nasal breathing, do it awake first. Close your lips, block one nostril for 30 seconds, then the other. If either side will not pass air comfortably, tape is the wrong tool and a clinician is the right one. If both are clear, you do not need tape either. You need to notice when your mouth is open.
How to check your own face instead of guessing
The features attributed to mouth breathing, a longer lower face and a wider jaw angle, are readings, not impressions. The jawline tool gives the jaw angle in degrees and the facial thirds tool gives the lower third as a percentage of face height. If you switch breathing habits, take the same photo under the same light three months apart. In an adult the numbers will not move, and knowing that is worth more than a roll of tape.
Sources
Rhee J et al., PLOS ONE 2025;20(5):e0323643 (systematic review, 10 studies, 213 patients). Harvold EP et al., American Journal of Orthodontics 1981;79(4):359-372 (rhesus monkey experiment). Warren DW et al., American Journal of Orthodontics and Dentofacial Orthopedics 1988;93(4):289-293 (nasal airflow in 116 adults). Batista KB et al., Cochrane Database of Systematic Reviews 2018;3:CD003452.