When you breathe, that same moist lining in your nose works to make sure that the air that reaches your lungs is well-humidified. So it follows that when your surroundings are dry, your nose has to work harder. A cold-mist humidifier, operating when the air is dry, helps moisturize airways and tissue linings.
Dr. Katz recommends that you fill the humidifier with distilled water to protect yourself from impurities in tap water. Also, be sure to clean the unit properly, according to the manufacturer's instructions, at least once a week.