Sinus Infection
Medical Author: Charles C. P. Davis, MD, PhD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
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:
- frontal sinus (in forehead),
- maxillary sinus (behind cheeks),
- ethmoid sinus (between the eyes), and
- 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."
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Sinus Infection
Cold, Flu, Allergy Treatments »
Introduction to cold, flu, and allergy treatments
Every year, millions of people use over-the-counter (OTC) products to relieve nasal
stuffiness and congestion, sneezing, runny noses, sore throat, and
cough. The common causes of these symptoms include the viruses that cause the common cold, influenza
virus, allergic rhinitis (hay fever), and sinus infections (sinusitis). Viral infections can also
cause headache, body aches, fatigue, and sometimes fever. Hay fever symptoms
can also include itchy eyes, nose, and throat, and watery eyes.
To benefit from OTC products for cold, flu, and allergy,
it is important to understand (1) the condition causing the symptoms, (2) the
predominant symptom(s) one wishes to
relieve, and (3) the active ingredient(s) in the product.
Some OTC products contain a single active ingredient
medication to relieve one symptom. Many others contain a
combination of two, three, and even four active ingredient
medications...
Read the Cold, Flu, Allergy Treatments article »
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