The nasal passage and trachea are the first and second lines of defense against irritants, dust and mold particles. Cold air dries out the respiratory tract’s protective lining (mucus and cilia – tiny hairs), increasing the capacity for irritants and pathogens to enter the airway ending in illness. Extreme cold air also increases airway-narrowing, as the bronchioles and alveoli are sensitive to temperature extremes, making breathing during exercise more challenging.