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During nasal breathing, heat and humidity are exchanged over a 160 cm(2) area of mucous membrane. This capacity is not sufficient for airway comfort during cold air breathing. Similarly, airway discomfort and constriction may be experienced during exercise-induced mouth breathing in marginally cold temperatures. In asthmatics and sensitive persons such airway discomfort rapidly transforms to broncho-constriction and related breathing problems. The Lungplus mouth-held breathing aid contains a coil of corrugated aluminium foil that provides a heat and moisture exchange area of 1200 cm(2) (Model 1) with a minimal breathing resistance. The present experiment was designed to quantify improved airway comfort using the device. Ninety-one subjects were exposed to each of three rooms with average air temperatures of +20, +3 and -15 degrees C, with a corresponding relative humidity of 50, 70 and 90%. For each condition, subjects gave subjective numerical assessments of the airway sensation during nose, mouth and Lungplus breathing, respectively. At each room temperature, mouth breathing resulted in a less comfortable airway rating than did breathing through the nose, which in turn resulted in a less comfortable rating than the Lungplus breathing condition.