What Causes Sinus Infections?


Quick Answer

Sinus infections are caused by viruses, bacterial and fungal growth, allergies and structural abnormalities in the nasal area. Sinusitis can also be caused by conditions that affect ciliary movement in the nasal passages, according to MedlinePlus.

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Full Answer

Sinus infections can be the direct result of swelling in the tissue lining the sinus passages and adjacent nasal mucosa, causing blockage. The swelling is most commonly caused by viral infections, such as the common cold, and allergies. The ethmoid and maxillary sinuses are involved most often. The blocked mucous in the sinus cavity provides a setting for bacterial, viral or fungal overgrowth leading to sinusitis, explains MedicineNet. Other causes of swelling are over-the-counter nasal sprays and cigarette smoke.

Less often, the sinuses are blocked by tumors. Fungal overgrowth is more common in immunocompromised individuals, although those with normally functioning immune systems can develop fungal infections from the soil after earthquakes or hurricanes, notes MedicineNet. Sometimes, sinus drainage can result from abnormally thickened mucous secretions. This happens in dehydration caused by cystic fibrosis that stiffens the mucous. Overuse of antihistamines and low-humidity climates can also thicken mucous secretions. Irritant-induced damage to the cilia that assist in mucous transport out of the sinuses can occur and result in mucous buildup and subsequent infection.

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