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Definition of Sinusitis

Sinusitis is inflammation of the mucous membrane lining the sinuses. This is usually more accurately termed rhinosinusitis, where “rhino” means nose, because inflammation in the sinuses is usually accompanied by inflammation in the nose. When the mucous membrane around the sinus openings (ostia) become obstructed, the sinuses fill with fluid creating a moist environment that is optimal for growth of micro-organisms such as bacteria. The infection causes further inflammation of the mucous membrane, creating a self perpetuating cycle.


  • Sinusitis is accompanied by many possible symptoms. The 4 most common symptoms are:
  • Nasal obstruction/congestion/fullness, which can cause difficulty breathing
  • Facial pain/pressure/fullness (including sinus “headache”)
  • Discolored nasal or postnasal discharge of varying colors and thickness
  • Decreased sense of smell

Other symptoms include fever, fatigue, bad breath (halitosis), cough, ear pressure, and tooth pain.

Acute sinusitis refers to a sudden onset infection, with fewer than 4 weeks of symptoms. The typical history of an acute sinus infection is a common cold that continues to worsen over several days, or initially improves followed by sudden worsening. Antibiotics are typically effective for treating acute sinus infections.

Chronic sinusitis refers to symptoms of sinusitis lasting longer than 12 weeks. These symptoms may not necessarily have started with an acute sinus infection, but patients with chronic sinusitis may also experience periods of infections characterized by worsened symptoms.

Recurrent acute sinusitis is diagnosed when patients experience 4 or more bacterial sinus infections each year. Patients who truly have this diagnosis without underlying chronic sinusitis are asymptomatic in between episodes, and typically have normal exams or negative CT unless done in the middle of an infection.

Causes of Sinusitis

An estimated 50 million people in the United States suffer from sinusitis. The number is thought to be continually increasing due to pollution, urban sprawl, and resistance to antibiotics. There are multiple causes of sinusitis which include anatomic, genetic, environmental factors, and other medical conditions. Often, a combination of these contributes to development of disease, although in many cases, every possible cause may not be identified.

Anatomic factors that cause sinusitis include variations in sinus cell development and deviated nasal septum, resulting in narrowing of the sinus drainage pathways. Environmental factors are pollutants such as tobacco smoke and chemicals, and allergens such as pollen, molds, dust mites, and pet dander. Genetic causes include cystic fibrosis and ciliary dyskinesia, leading to abnormal mucus production and clearance. Specific genes involving immune system elements may be involved and research is ongoing to further characterize these genes.

Various medical conditions also contribute to or are associated with sinusitis. Greater than 1/3 of patients with asthma also have sinusitis. Immunocompromised states such as poorly controlled diabetes, human immunodeficiency virus (HIV) infection, or recent chemotherapy may also contribute. Sinusitis may also be caused by tissue growths blocking the sinus drainage pathways, including polyps and tumors.