At the extremes of temperature and humidity, the lungs must condition the inspired air to match alveolar conditions of 100% saturated with water at body temperature. The nose plays a key role at rest or with mild exercise, but the lower airways are also involved at higher levels of hyperpnea. The healthy lung usually handles this added stress without difficulty, but people with asthma may have exercise-induced bronchospasm from the relative cooling and drying of the airways that trigger an inflammatory response and airway narrowing. Repeated exposure to cold, dry air may result in airway irritation, inflammation, and injury, and is relevant to cold-weather athletes as well as patients on mechanical ventilation or with a laryngectomy. Even in healthy individuals, lung function may be adversely affected by environmental temperatures or humidities that are too extreme, and patients with underlying respiratory disease may have exacerbation of symptoms from such exposures. Extremes of environmental temperature and humidity may compound the adverse effects of air pollution or aeroallergens and pollen, and thus be especially pertinent as we experience climate change, further worsening pulmonary symptoms and lung health.