It may surprise you that breathing primarily through the mouth instead of the nose can actually have some pretty negative effects on health, including oral health. Mouth-breathing should only be done as an emergency backup, not the main way to breathe.
The nose has a built-in filtration system and triggers nitric oxide production, helping our lungs absorb oxygen better. We don’t get any of that from mouth breathing. Short-term effects of mouth breathing include dry mouth, reduced oxygen levels, and impaired speech. Dry mouth is particularly dangerous for dental health, because saliva is the teeth and gums’ first line of defense against bacteria and acid. We also need saliva to taste our food!
Children who grow up breathing mainly through their mouths can actually develop differently, their faces becoming flatter, with weaker chins and droopy eyelids as they grow up. They are more likely to have complex orthodontic problems, with narrow arches and lots of crowding. Other long-term effects for habitual mouth-breathers include an increased likelihood of sleep apnea, which in turn comes with low energy, poor concentration, and a weaker immune system.