Sinusitis is an inflammation of the sinuses — the hollow spaces in the nasal cavity — that causes mucus to build up and bacteria to grow. This creates pressure and pain around the person’s eye sockets, forehead or cheeks, and if not treated, it can lead to other more severe complications. The most common causes of sinusitis, also known as a sinus infection, are viral infections, bacterial infections, allergies and asthma. Abnormalities in the sinuses, fungal infections, temperature changes, air quality and dehydration are also common causes of sinusitis.
Sinusitis is most commonly caused by a bacterial infection. When a person contracts a cold or flu virus, they usually become congested as a result of the nasal passages becoming inflamed. A cold or flu can be the underlying cause of sinusitis, but most sinus infections develop as a result of a bacterial infection that develops. Bacteria that are normally released in mucus become trapped in the nasal cavity and begin to grow and spread, causing an infection in the sinuses. The most common types of bacterial sinusitis are caused by Streptococcus pneumoniae, H. influenzae, Moraxella catarrhalis and Staphylococcus aureus.
Asthma and allergy attacks can also be a cause of sinusitis. The sinuses become inflamed because of allergens in the air, pollution, smog and cold temperatures. These triggers are much more likely to affect someone who is already allergic to or sensitive to substances in the air, such as dust, smoke or dander. People suffering from asthma already have a weakened upper respiratory system, and they naturally have difficulty releasing mucus from their nasal cavity.
Abnormalities in the sinuses are also common causes of sinusitis. A person with narrow sinuses or larger than normal adenoids — the masses of tissue on the back of throat that connect to the nose — are more likely to contract sinusitis because these abnormalities regularly cause blockages in the nasal passages. Nasal polyps and a deviated septum are also abnormalities that can cause blockages in the nasal passages.
Other less common causes of sinusitis include dehydration and fungal infections. If a person is dehydrated, mucus will become thick and may block the nasal cavity. If a person inhales or ingests a fungus, it can cause inflammation because of an allergic reaction to the fungi. Fungal sinusitis more commonly affects people with impaired immune systems from conditions such as diabetes or AIDS.