When exercising, should you breathe through your nose, mouth or a combination of both if you have asthma?

Nose. In general, breathing through your nose humidifies and warms the air you inhale, making it more gentle to your airways.
Nose. The nose warms and humidifies the air we breath. Breathing cold air can trigger bronchospasm/asthma in some patients with asthma, so breathing through the nose is best to avoid the direct introduction of cold air to the lungs.