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Sinusitis is an inflammation or swelling of the mucous membranes that line the sinus cavities, air-filled spaces in the bones of the face that are connected to the nasal passages. This swelling can interfere with normal sinus drainage, cause increased mucus production, and lead to bacterial infection. Sinusitis can emerge from a bout with the common cold or can be the result of long-term inflammation. Sinuses can be inflamed for many reasons, such as viral infection, allergies, or smoking; if untreated, this inflammation can get worse over time and cause symptoms like nasal obstruction, facial pressure, coughing, and postnasal drip that won't go away.

Health experts estimate that 37 million Americans are affected by sinusitis every year-and spend nearly $6 billion annually on the costs of battling it. Sinusitis is usually more uncomfortable than dangerous, but in very rare cases, infection can spread from the sinuses to the bones or even the brain.

Acute sinusitis often goes away in a few weeks, either on its own or after treatment with antibiotics, decongestants, or washing out the nose with salt water. If sinusitis lasts less than four weeks, it is considered acute sinusitis. However, for many people, sinusitis is a chronic problem. For these people, longer-term medicines or even surgery may be necessary.

This section offers more on:

  • Need-to-know anatomy
  • Causes
  • Risk factors
  • Need-to-know anatomy

    Sinuses are air-filled cavities in your head. They are part of the upper respiratory system. The function of sinuses is not well understood; they may be involved in warming air before it reaches the lungs, or may have evolved because they alter the resonance of our voices.Adults and older children have four groups of sinus cavities (maxillary, ethmoid, frontal, and sphenoid) inside the bones surrounding the nose. Very young children have small sinus passages and cavities rather than fully formed sinuses. The sinuses are lined with mucous membranes that join up with the mucous membranes lining the nose. Under normal conditions, the sinuses produce up to 1.5 liters of mucus per day! Each sinus cavity has one or more openings into the nose to allow for drainage of this mucus and flow of air.


    Sinusitis can be either acute or chronic. Acute sinusitis is often caused by a viral respiratory infection that in some cases leads to a bacterial infection; the condition is short term, resolving once the infection has run its course.Usually, the sinuses do not have bacteria in them, but they are connected to the nose, which does normally harbor bacteria.

    To avoid infection, the sinuses need adequate mucus drainage and a functioning immune system. Each sinus cavity has an opening into the nose to allow for drainage of mucus. But anything that causes swelling in the nose may lead to obstruction or blockage of the sinuses, which can cause a feeling of pressure and lead to infection. This includes chronic inflammation in the nasal passages, such as that caused by allergies. In fact, inflammation of the nose and sinuses is believed to be the most important factor causing both acute and chronic sinus problems for patients.

    The common cold and other viral respiratory illnesses, allergies, and factors in the environment such as air pollution are the most common triggers for the development of sinusitis. These can all increase mucus production, change the characteristics of the mucus, and cause swelling in the nose and sinuses. The point at which the common cold ends and a sinus infection begins is not always easy to determine.

    Other important factors may include tobacco exposure; a deviated septum, in which the piece of cartilage or bone between the nostrils is severely off-center; nasal polyps, which are usually caused by chronic inflammation; dryness, and mold sensitivity.

    Diseases such as asthma, cystic fibrosis, bronchiectasis (a disorder of the airways within the lungs), immune deficiencies, and immotile cilia syndrome (a rare genetic disorder in which cells can't move mucus effectively) are often associated with sinusitis. In many people with sinus problems, the lining of the nose and sinuses is overly sensitive or "reactive" to a variety of factors. Thus there are multiple possible triggers for the development of inflammation causing sinusitis.

    Risk factors

    People with allergies, asthma, and nasal polyps are more likely to develop sinusitis. Many people with asthma also have chronic sinusitis. People with deficient immune systems, such as those with HIV, are more likely to have sinus problems. Also, people with cystic fibrosis or other problems with the movement of mucus are likely to have sinusitis. Living in an area with large amounts of pollen or pollution in the air can also increase the risk in sensitive people.

    Last reviewed on 10/14/09

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