When you breathe through your nose a chemical called nitric oxide is released. Nitric oxide basically expands the blood vessels, meaning that more blood can flow through them. More blood flowing through means more oxygen can be transported through the system where it is used to make fuel for your body’s performance and healthy functioning. 

Nitric oxide is also anti bacterial and anti viral, which means it helps the immune system fight off the bad guys that can impact your health. All that, just from breathing through your nose.