The nose is meant for breathing, and the mouth is the backup plan in case something goes wrong with the nasal passages. As infants, humans are predisposed to breathe through their nose, so much as they are referenced as obligated nasal breathers. Infants can breathe through both their nose and mouth, but according to a LiveStrong article on the topic, “oral breathing is potentially difficult because the soft palate –a muscular fold that extends from the back of the roof of the mouth–is so close to the epiglottis–a flap of cartilage that covers and protects the windpipe during the act of swallowing”.
As humans, we learn to breathe through the mouth when we are sick with colds and sinus problems, and turn to the learnt habit of oral breathing over time. It doesn’t feel like a huge difference, as oxygen is still entering the body. But the nose is designed to take part in respiration mores than the mouth, which has many other functions, such as speaking and swallowing.
The respiratory system is broken down into two zones, the conducting zone and the respiratory zone. The nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles all work together to filter, clean, moisten, and dry the air that we inspire before sending it, or conducting it, to the respiratory zone and the lungs. Therefore, medically speaking, the nose built to serve as the entrance and exit point for breath.
The art of yoga breathing does have a name – Pranayama. Most yogic practices favor the use of nasal breathing, although some practices find ways to incorporate the use of oral breathing as well. Ever had a yoga teacher ask you to breathe in deeply through the nose, followed by a strong exhale with a wide open mouth? Techniques vary, but overall, there is much more of a focus on the benefits of nasal breathing and learning controlled breath through Pranayama.