Face masks or respirators are commonly worn by medical professionals and patients for protection against respiratory tract infection and the spread of illnesses, such as severe acute respiratory syndrome and pandemic influenza (H1N1). Breathing discomfort due to increased breathing resistance is known to be a problem with the use of N95 respirators but there is a lack of scientific data to quantify this effect. The purpose of this study was to assess objectively the impact of wearing N95 face masks on breathing resistance. A total of 14 normal adult volunteers (seven males and seven females) were recruited in this study. Nasal airflow resistance during inspiration and expiration was measured using a standard rhinomanometry and nasal spirometry. A modified full face mask was produced in-house in order to measure nasal resistance with the use of N95 (3M 8210) respirators. The results showed a mean increment of 126 and 122% in inspiratory and expiratory flow resistances, respectively, with the use of N95 respirators. There was also an average reduction of 37% in air exchange volume with the use of N95 respirators. This is the first reported study that demonstrates quantitatively and objectively the substantial impairment of nasal airflow in terms of increased breathing resistance with the use of N95 respirators on actual human subjects.