Breathing through your mouth while running may allow you to take in more air, but it’s not necessarily a good thing. In winter, a large amount of cold air entering the trachea and throat can easily cause coughing, tracheitis, or abdominal pain; in spring, inhaling through the mouth draws dust and bacteria directly into your body, which can also lead to other diseases.
       Use only nasal breathing during warm-up runs
       In the initial stage of running or when running at a very slow pace, you should breathe through your nose. The nasal cavity is rich in blood vessels that can slightly warm the incoming air; the nasal mucosa secretes fluid that increases the humidity of the air; and nasal hair along with secretions from the nasal mucosa can block and filter out dust and bacteria, offering some protection to the respiratory tract.
       Use both mouth and nose breathing during mid-run
       After running a certain distance or increasing your speed, the amount of air you need to ventilate per unit of time can increase several to dozens of times compared to when at rest. Breathing through the nose alone won’t be sufficient, and you may feel breathless and uncomfortable — this is when you’ll need to use your mouth as well. When using both nose and mouth, be careful not to breathe with your mouth wide open. Instead, you should breathe in through the nose and out through the mouth, using the mouth only for exhalation. The method for exhaling through the mouth is: slightly part your lips, gently clench your teeth, curl the tip of your tongue, and let it lightly touch the roof of your mouth, allowing air to be pushed out through the gaps between your teeth. When breathing, ensure it is even and rhythmic. Exhale with short, strong bursts and appropriate depth; inhale slowly and evenly.