UC San Diego

Carbon dioxide inhaled through the nose in concentrations above 10% evokes nasal irritation. As concentration is increased, a non-systemic, reflexive interruption of inhalation eventually occurs in most persons. This study revealed that smokers have a considerably higher threshold for the reflex. The elevation of threshold occurred to a comparable degree in both male and female smokers, although females generally had a lower threshold than males. It therefore appears that smokers have less sensitivity to nasal irritants. This marks the first instance of a substantial chemosensory difference between smokers and nonsmokers.