The nose functions to warm, humidify, and filter the air that we breathe. To understand the problems that can develop in the nose and sinuses, it is helpful to understand how it normally works.
Inside the nose, in the center, is a partition separating the two sides of the nose. This is the septum. The septum is made of a thin sheet of cartilage and bone, covered by a lining called mucosa. Ideally, the septum will be straight and thin. Problems occur if the septum is bent or too wide, or if there are large irregularities or spurs. A crooked septum, or one that is wide or thickened, is referred to as deviated. A septum may become deviated due to injury, or may simply develop that way from birth.
On the sides of the nose are structures called turbinates. These are curved shelves of bone covered by a special type of mucosa which is able to enlarge greatly when the body allows more blood to enter the tissue. The main job of the turbinate is to regulate the warming, humidifying, and airflow functions of the nose.
Turbinates will swell in response to infections, allergies, or other irritants. Irregular airflow from a deviated septum will cause the turbinates to slowly enlarge. They also swell somewhat when you lie down, which is why many people will notice that their breathing is worse at night. Finally, the body will naturally cause the turbinates on one side to be relatively swollen for a 4 to 5 hour period, following which the other side will swell. This is why many people with airway problems will notice that they can breathe through one side part of the time, and the other side at other times.
The large turbinates in the lower part of the nose are called the inferior turbinates. When these are enlarged, breathing is blocked. The next set of turbinates is called the middle turbinates. These turbinates are in front of the openings into the sinuses. When they are abnormal they can block the sinus openings, leading to pressure, pain, or infection. The superior and supreme turbinates are tiny, and usually do not cause problems.