Sinus Infection

Medical Author: Charles C. P. Davis, MD, PhD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

• What is a sinus?
• What is a sinus infection?
• What causes sinus infections?
• What are the types of sinusitis?
• What are the symptoms of sinus infection?
• How is sinus infection diagnosed?
• How is sinus infection treated?
• What are complications of sinus infection?
• Can sinus infection be prevented?
• Sinus Infection At A Glance
• Related sinus infection article:
  Sinus infection - on eMedicineHealth
• Pictures of Sinusitis (Sinus Infection) - Slideshow
• Patient Discussions: Sinus Infection - Effective Treatments
• Find a local Ear, Nose, & Throat Doctor in your town

What is a sinus?

A sinus is a hollow, air-filled cavity. For the purposes of this article, a sinus will referred to those hollow cavities that are in the skull and connected to the nasal airway by a narrow hole in the bone (ostium). Normally all are open to the nasal airway through an ostium. Humans have four pair of these cavities each referred to as the:

1. frontal sinus (in forehead),
2. maxillary sinus (behind cheeks),
3. ethmoid sinus (between the eyes), and
4. sphenoid sinus (deep behind the ethmoids).

The four pair of sinuses are often described as a unit and termed the "paranasal sinuses." The cells of the inner lining of each sinus are mucus-secreting cells, epithelial cells and some cells that are part of the immune system (macrophages, lymphocytes, and eosinophils).

Functions of the sinuses include humidifying and warming inspired air, insulation of surrounding structures (eyes, nerves), increasing voice resonance, and as buffers against facial trauma. The sinuses decrease the weight of the skull.

Picture of the anatomy of the sinuses

What is a sinus infection?

A sinus infection occurs when a pathogenic organism (virus, bacterium, or a fungus) grows within a sinus and causes intermittent blockage of the sinus ostium. Drainage of mucus and pus often occur when the blockage is relieved. The drainage usually goes from the nasal passages to the throat or out the nostrils. Such infections also cause inflammation (an influx of immune cells and swelling of the sinus tissue) of one or more sinuses. This adds to blocking the openings of the sinuses and causes discomfort.

Inflammation of the air cavities within the passages of the nose (paranasal sinuses) is referred to as sinusitis. Sinusitis can be caused by infection, but can also be caused by allergy and irritation of the sinuses.

Sinusitis is one of the more common conditions that can afflict people throughout their lives. Sinusitis commonly occurs when environmental pollens irritate the nasal passages, such as with hay fever. Sinusitis can also result from irritants, such as chemicals or the use and/or abuse of over-the-counter (OTC) nasal sprays, and illegal substances that may be snorted through the nose. About 30 million adults have "sinusitis."

Next: What causes sinus infections? »