Causes and Risk Factors of Sinus Infection

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A sinus infection (sinusitis) can develop after sinus inflammation due to a cold or allergy. Acute sinusitis lasts 10 days to four weeks and can be viral or bacterial. When the inflammation and symptoms last 12 or more weeks, it is called chronic sinusitis and is often due to ongoing inflammation, allergies, irritants, or structural blockages, but can be caused by a fungal infection. Both children and adults can have acute or chronic sinusitis. Learning more about what causes sinus infections may help you prevent them—or at least be more aware of the possibility that one is on the way.

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Common Causes

Acute sinusitis often starts with an upper respiratory infection, such as a cold, that leads to inflammation and congestion in the nasal passages and sinuses. Allergies, including hay fever, can also cause sinus inflammation. When the mucous membranes in the sinuses become inflamed they swell, making it difficult for them to drain. Excess mucus or thick mucus can clog the sinuses, causing pressure and pain. The inability of the sinuses to drain and the associated lack of airflow create an environment that is ideal for bacterial growth.

Acute Viral Sinusitis

In acute viral sinusitis, the virus that caused the upper respiratory infection has infected the sinuses and continues to produce mucus, inflammation, and congestion. This type of acute (or subacute) sinus infection can linger for up to 10 days before getting better.

Acute Bacterial Sinusitis

In acute or subacute bacterial sinusitis, the bacteria growing in the congested sinuses now produce ongoing symptoms. The infection may have started with a virus, or the congestion could have been due to an allergy attack or other irritants. If the symptoms have continued beyond 10 days and are not improving, or they got better, then got worse, it is likely that a bacterial sinus infection has developed.

Fungal Sinus Infection

It is also possible for your sinuses to become infected with a fungus. One type of infection is a non-invasive fungus ball, usually caused by the fungus Aspergillus. The fungus is normally found in the air but doesn't usually live inside the body. The presence of dead inflammatory cells, mucus, and debris in your sinuses allows the fungus to begin to grow there, but it doesn't invade your living tissues. This produces the usual sinusitis signs of nasal congestion, headache, and sinus pressure.

Other types of fungi may be present in the air, but they don't usually invade living tissues. When they do, an invasive fungal sinus infection can occur; this more often happens in people with weakened immune systems. As the fungus grows it causes more severe symptoms as it affects nearby structures.

Another type of sinus infection, granulomatous invasive fungal sinusitis, occurs mostly in the Sudan, India, and Pakistan and affects people who appear to have normal immune systems.

Invasive fungal sinus infections often become chronic (lasting longer than three months). They can be difficult to treat and may require sinus surgery and antifungal medications to resolve.

Chronic Sinus Infection

Chronic sinusitis can develop after repeated upper respiratory viral infections. However, the link between these infections and ongoing sinusitis isn't clear—and the virus may not be what's causing the chronic problem.

More often, chronic sinus infection is due to inflammation that can be caused by allergies or irritation from things in the air. Any allergy that causes inflammation or congestion can lead to sinusitis, but allergies to things present year-round (dust mites, animal dander, molds, cockroaches) can be especially problematic.

In particular, allergies to fungus are associated with the development of chronic sinusitis because fungal allergies cause the mucus to become abnormally thick. The most common types of fungi that trigger these allergies are Alternaria, Cladosporium, Aspergillus, Penicillium, and Fusarium. The fungus present in the air can become entrapped in the thick mucus and continue to set off the allergic reaction.

Structural abnormalities can also contribute to chronic sinusitis. Enlarged turbinates (concha bullosa), deviated septum, enlarged adenoids, and nasal polyps can inhibit proper ventilation and airflow. Nasal polyps are masses of benign tissue that grow inside of the sinuses and nasal passageways. Ironically, having chronic sinusitis in and of itself can lead to diseased tissue or abnormal growths like nasal polyps. These problems may need to be surgically repaired.

Aspirin-exacerbated respiratory disease (AERD) is a syndrome that includes chronic sinusitis, asthma, and aspirin allergy. People with AERD often have nasal polyps. They can have severe sinusitis that affects all of the sinuses.

Health Risk Factors

Allergic rhinitis is a risk factor for both acute and chronic sinusitis. If you have environmental allergies, you should try to avoid your exposure to the triggers. You should have your allergies fully diagnosed and identified so you know what to avoid. You can also work to maintain better control of your allergies so your airways are not inflamed and congested.

If you have a weakened immune system, you may be at additional risk for acute or chronic sinusitis. This includes anyone with HIV/AIDSmultiple myeloma, blood cancers, or chronic disease, or who are undergoing treatment with corticosteroids or chemotherapy, for example. Your body not only has a hard time fending off infections that can lead to sinusitis, like the common cold but recovering from a sinus infection if one takes roots. Fungal allergies that can lead to sinusitis are particularly more common in those with a weakened immune system. 

Other conditions that are associated with the development of chronic sinusitis include gastroesophageal reflux disease (GERD), asthma, non-allergic rhinitiscystic fibrosis, Kartagener's syndrome, and various autoimmune issues.

Lifestyle Risk Factors

There are risk factors you can influence so you may be able to avoid acute or chronic sinus infections.

Environmental Toxins

Inhaled environmental toxins can contribute to chronic sinusitis. Formaldehyde is one such toxin you may be exposed to through occupations such as laboratory worker, manufacturing worker, woodworker, furniture maker, and mortician. Air pollution, in general, may increase the risk.

Smoking and Secondhand Smoke

Probably the most common environmental toxin associated with chronic sinusitis is tobacco smoke. Cigarette smoke adversely affects the specialized cells that line the airway. The hair-like cilia lining the airways and nasal passages can become paralyzed and can't sweep away mucus and harmful substances. This can lead to chronic inflammation.

You should stop smoking if you have chronic sinusitis, and this will also reduce your risk of acute sinusitis. Smoking cessation can reverse or partially reverse some of these problems, with results varying between individuals and somewhat depending on how long you have smoked.

Exposure to secondhand cigarette smoke can be just as harmful, (or more so), and children living in homes where another family member smokes indoors are at an increased risk for ear, nose, and throat disorders.

Dry Air

Dry indoor air, such as from air conditioning or forced air heating, can contribute to the risk of sinusitis. Normally, a layer of mucus in the nasal passages traps irritants and they are swept out by the hair-like cilia that line the passages. Dry air is thought to hamper this process and result in increased irritation. You can use a humidifier to reduce this risk. However, you will need to keep it clean as mold growth can contribute to allergies.

Exposure to Respiratory Infections

Catching a cold is one of the biggest risks of developing a sinus infection, so preventing the spread of colds can help reduce your risk. Be sure to wash your hands frequently we soap and water, especially before you eat.

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