Mouth tape.

"Mouth taping is taping your mouth shut when you go to bed at night, and I made a video cautioning against this practice before because it can be very harmful to your health. People who sing the praises of mouth taping claim all sorts of benefits that it helps you remember to breathe through your nose more, you get better sleep. There are benefits to breathing through your nose like it helps to filter out allergens, it helps to moisturize the air, and it helps to reduce dry mouth from mouth breathing, but what they don't tell you is that why are you breathing through your mouth in the first place when you sleep? It might be because you have something going on in your nose that limits nasal breathing properly, for example maybe you have a deviated nasal septum or maybe have nasal polyps, something that's actually really common in people who have allergic conditions like asthma. If you've been breathing a lot through your mouth it may be because you have enlarged tonsils. So by taping your mouth shut you may not be allowing yourself to get adequate oxygenation to your brain at night leading to apnea. The benefits of mouth taping are not substantiated by evidence. There is a small amount of research that suggests it might be helpful in certain circumstances but that research is not conclusive."

"I decided to just try it because I was sent some mouth tape in PR. I was like, why not just see what the hype is about? And I'll tell you, I actually really like it. Not because I think it's changing the shape of my jaw, but because it keeps my mouth shut the whole time, and I find I wake up with less dry mouth in the morning. It does keep the mouth more moist and that helps to prevent cavities too, because if it's really dry then you're more cavity prone."