On either side of your nasal cavity are large sinuses followed by a row of small sinuses behind the bridge of the nose. When you get sinusitis, these large sinuses inflame and get infected due to bacterial, viral or fungal action. There can also be non-infectious inflammation in the sinuses that can be acute or chronic depending on the duration.

The risk of getting sinusitis is increased in patients who have immunity issues. For instance, patients with diabetes, cystic fibrosis, AIDS etc. are at a higher risk compared to others. There are also people born with a malformed septum, who can get sinusitis.

The infections in the sinus can be caused due to many reasons such as these:

• Untreated allergies is one of the main contributing factor. They can cause the infections to develop in the sinus and become chronic over a period. People with sensitivities to certain foods can also develop sinusitis.
• Bacterial invasion is the next cause of sinusitis. It can occur within one or more of the sinus cavities. The bacteria that enter the nasal passages and sinus cavities through the air get trapped by the mucus secreted by the membranes surrounding these areas. Bacteria such as Moraxella catarrhalis, Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus along with some anaerobes etc., when trapped in the mucus can cause severe infection.
• Another parasite that can cause infection in the sinus are fungi. Fungal infections are just as dangerous as bacterial ones.
• Abnormalities such as malformed septum mentioned above or trauma related injuries to the nasal cavity can cause the mucus to accumulate in the sinus cavities. This excess mucus can form breeding grounds for bacteria and fungi.
• Cold or flu-like illness can also lead to sinusitis. The viruses that cause cold or flu can spread to the sinuses causing viral sinus infection. In certain cases, bacteria can also add onto the infection that was started by the virus making it worse and last longer.
• Yet another cause of sinusitis is a spread from a dental infection. The infection from an infected tooth spreads to the maxillary sinus causing sinusitis.
• Abnormalities in the auditory or Eustachian tube can result in chronic sinusitis as well. This tube is connected to the sinus cavities and the throat. It is usually level with the eye sockets but abnormality is present, it can be at the same level as the vestibule or nasal entrance. This can invite infections.
• Being aware of the above factors can tell you the reasons why your sinus has obtained the infection. This can also help the physician to decide on the proper course of action regarding your treatment.