A method of automatically controlling the humidity of a gas stream of a pressure support system (50) during use of the system is provided. The method includes receiving a first humidification level, and controlling operation of a humidifier (68) based on the first humidification level and at least one of: (i) one or more environmental parameters relating to environmental conditions around the pressure support system, (ii) one or more gas stream parameters relating to a gas stream output by the pressure support system to a patient circuit (56, 58), (iii) one or more respiratory demand parameters of a user of the pressure support system, and (iv) one or more operating parameters of the pressure support system that effect a flow rate that is generated by a pressure generating system (52, 60) of the pressure support system.
