Comment by array_key_first

You can generally see who has sleep apnea just by looking at their face - there's a particular anatomy that comes with heavy mouth breathing and obstructive sleep apnea. If you speak to people who have obstructive sleep apnea, virtually all of them report mouth breathing and mouth dryness.

I think, probably, there's some structural elements that can make mouth breathing more attractive or easier. But, mouth breathing doesn't actually work well for the breathing part. So, for those people, they experience obstructive sleep apnea. For others, they don't. I have spoken to sprinters who have told me that even sprinting is easier to do with nose breathing. But, for others, they cannot even sleep while nose breathing.

So, I definitely believe there are structural elements at play with breathing.