The nose has an area of specialised cells which are responsible for smelling (part of the olfactory system). Another function of the nose is the conditioning of inhaled air, warming it and making it more humid. Hairs inside the nose prevent large particles from entering the lungs. Sneezing is usually caused by foreign particles irritating the nasal mucosa, but can more rarely be caused by sudden exposure to bright light (called the photic sneeze reflex) or touching the external auditory canal. Sneezing is a means of transmitting infections because it creates aerosols in which the droplets can harbour microbes.
Airway obstruction is a respiratory problem caused by increased resistance in the bronchioles (usually from a decreased radius of the bronchioles) that reduces the amount of air inhaled in each breath and the oxygen that reaches the pulmonary arteries. It is different from airway restriction (which prevents air from diffusing into the pulmonary arteries because of some kind of blockage in the lungs).