The nose and sinuses form the first part of the respiratory system, the body system that exchanges gases between air and blood. The nose is the main organ that allows air to flow into the lungs. Air enters the body here through two passageways (the nostrils). Each nostril opens up into its own nasal cavity (large spaces inside the front of the face).

The most important function of the nose and nasal cavity is to process each breath before it enters the lungs. This includes:

• Filtering out dangerous particles (e.g., bacteria, viruses, dust, pollen)
  
  
• Warming each breath to prevent cold air from damaging sensitive lung tissue
  
  
• Adding moisture to each breath to prevent airways and lungs from drying out

In addition, the nose is part of the olfactory system, which senses smell.

The sinuses are air-filled pockets found within the bones of the nose and face. The sinuses appear in pairs on either side of the face. There are four different types of sinuses and, depending on the type, they vary in size from tiny to the size of a walnut. The precise role of the sinuses remains unclear, although they are believed to serve several functions, including:

• Reducing the weight of the skull while preserving bone strength and shape
  
  
• Adding resonance to the voice
  
  
• Reducing damage sustained during a head trauma by absorbing some of the impact

The nose, nasal cavity and sinuses are the first few components of the respiratory system. The respiratory system is also made up of the pharynx, (the passageway at the back of the throat), larynx (voice box), trachea (windpipe), bronchi (bronchial tubes) and lungs.