It runs vertically along the midline of the nose and divides it into two cavities, referred to as nasal fossae, that determine the easy or difficult passage of air.

These nasal cavities are responsible for the filtering of air and the correct temperature and moistness of the air.

It has two functions: to act as a support to the external part of the nose (cartilaginous) and as a separating wall between the more or less equal nasal cavities The correct functioning of the air is extremely related to the fact that the size of the two nasal cavities are approximately equal.

Deformity and distortion of the nasal septum are often the cause of breathing problems, when air passing through the nose may be entirely or partially blocked. The nasal septum may be distorted due to traumas as a result of falls, during games, accidents or for congenital causes (present at birth).

Both the nasal cavities as well as the nostrils are lined with a mucus mantle and also the nostrils are lined with hair called vibrissae. Mucus and vibrissae prevent fine dust and small foreign bodies from passing through to the respiratory channels with the air that is breathed; the nasal mucus furthermore moistens the incoming air (especially of the turbinates).

If the passing of air through the nose is impossible or hindered, the nasal function gets blocked and breathing is done through the mouth, with the consequential emission into the lungs of improperly filtered and non-moistened air. The hindrance to normal breathing through the nose may cause diseases such as rhinitis, sinusitis, complications of the ear and oral cavity pathologies and also vocal cord pathologies, due to the lack of nasal filters.

The deviation of the nasal septum may be corrected with suitable surgical procedures of septoplasty or septorhinoplasty (should the septum determine also a distortion of the nasal pyramid).