Causes of Sinusitis

In this article Sinus Doctor answers :

What are the Main Causes of Sinusitis Infection? Sinusitis can be caused by a variety of reasons ranging from microorganisms & allergies to polyps to structural abnormalities such as a deviated septum to some rare causes such as carcinomas. This article is going to be detailed and technical because it is important to understand the wide range of causes of Sinusitis and why proper diagnosis and timely treatment is crucial.

Why it is important to understand the plethora of causes of Sinusitis?

Chronic sinusitis is one of the most common chronic diseases in humans. Most of the patients never get to a comprehensive ENT examination but seek help and remain in the realm of primary medical care. The reasons for this are many. Shortage of specialized medical care and mild clinical presentation are probably among the most important ones.

Although primary care physicians are trained to treat it, they often don’t have access to all the diagnostic tools necessary for adequate assessment of a patient with chronic sinusitis. This is why many patients are unaware of the structural abnormalities and conditions that pose a root cause of their health problems. They respond well to the medicines, or at least well enough to lose interest in further diagnostics and treatment. So, instead of undergoing a surgery that can bring them a permanent relief, patients stay trapped in a lifelong episode of chronic sinusitis.

More to the point, some of the root causes we will talk about require immediate surgical intervention because if left untreated can turn into malignancies and put the patient’s life at risk.

Minimally invasive surgery reduced the risk of infection and other complications. It revolutionized ENT surgery- scars are a matter of the past now. However, when it comes to better outcomes, it’s all about a timely diagnosis. A malignancy in the face and neck region that’s well under its way cannot be treated using a minimally invasive approach. This is why it is so important to recognize and resolve the problem before it becomes untreatable.

Different agents such as bacteria, viruses or chemical particles such as cigarette smoke can trigger an episode of Sinusitis.

The lining of sinuses is metabolically and functionally a very active structure – it secretes mucus continuously and the cilia continuously ‘push’ the mucus through canals and into the nasal cavity. The canals also let the air in and out of the sinuses, thus maintaining the process of their ventilation.
Whenever any of the three key points of sinus health (mucus production, drainage, and ventilation) are interrupted, the risk of infection increases.

Microorganisms that cause Rhinosinusitis

  • Viruses
    Viruses are the most common cause of Sinusitis. Actually, research shows that in more than 95% of cases, viruses are to blame. Luckily, viral infections are typically self-limiting, meaning our immune system finds a way to fight them off. Viral Sinusitis usually lasts 7 days, 10 at most.
  • Bacteria
    Bacteria are a far less common cause than viruses. Worsening symptoms up to five days after the onset of Sinusitis and if persistently lasting for over 10 days, it is highly suggestive that bacteria are the causing factor. Although most episodes resolve on their own (even without medications), to stay on the safe side and avoid complications, doctors often prescribe antibiotics if they suspect bacterial infection.
  • Fungi
    Fungi is a rare cause of Rhinosinusitis. According to research, not more than 2% of all patients diagnosed with Rhinosinusitis suffer a fungal infection. Quite often, fungal infections of the upper respiratory tract are caused by prolonged use of antibiotics or a weakened immune system (a condition known as Immunodeficiency).

Non-infective agents, diseases and chemical substances that increase the risk of Rhinosinusitis

  • Allergies
    Allergic Rhinosinusitis has a seasonal character – meaning, the patient has problems only during the allergy season. The allergy often affects other organs, so besides typical Rhinosinusitis symptoms, patients complain of watery eyes, tingling sensation in the nose, sneezing, etc. The swelling of mucus membranes of the upper respiratory tract and mucus buildup create favorable conditions for bacterial infection.
  • Cigarette smoking
    Numerous research studies have established that cigarette smoke has detrimental effects on human health. The lining of the upper respiratory tract (including sinuses) is the first to suffer the consequences of smoking by losing its cilia and consequently, the ability to clean the surface of the airways effectively. Over time, toxic compounds from cigarette smoke dissolve and pile up in the trapped mucus of the sinuses. Other than inflammation, the pile-up of toxic waste can lead to Cancer too!
  • Diabetes Mellitus
    People with poorly regulated diabetes are at a higher risk of Sinusitis compared to the healthy population. The reason lies in the fact that diabetes weakens the immune system and causes subtle changes in the tiny blood vessels around the body, which in some people lead to impaired functioning of the lining inside the respiratory system, including sinuses.
  • Dental infections
    The upper teeth and maxillary sinuses are in close anatomical relation. So every process that affects the upper teeth can get out of control and spread to the sinuses. In some people, teeth roots protrude into the sinus cavity. After extraction, the communication between the sinus and mouth establishes, which opens a path to the infection. This is why tooth extraction followed by frequent sinusitis episodes always should bring suspicion that the maxillary sinus may have ‘opened.’
  • Swimming, diving, hiking at high altitudes
    Activities performed in the environments where outside pressure is somehow changed (increased or decreased) affects the mucus secretion from the surface of the respiratory tract, including sinuses. As a result, mucus builds up, the sinus drainage is not as effective, which together increases the chances of infection and subsequent rhinosinusitis.
  • Septal and other anatomical deviations of the upper respiratory tract
    Septal deviation is one of the most common anomalies seen in humans. The septum is a bony structure that separates the left and right halves of the nasal cavity. In cases where it deviates to one side (a condition that may be inherited or acquired after an injury), mucus can build up in sinuses causing frequent episodes of sinusitis. Generally speaking, the treatment of all anatomical abnormalities in ENT is surgical. Those abnormalities are often a direct cause of severe recurrent rhinosinusitis episodes.

Rare causes

Other scarce conditions such as cystic fibrosis, immotile cilia syndrome and few others may cause Sinusitis.

Structural abnormalities that cause Sinusitis

Structural abnormalities of the nasal septum, paranasal sinuses, and the lining are a common cause of chronic sinusitis. We have a detailed article on how Structural abnormalities cause Sinusitis here.

Polyps and Tumors

  • Antrochoanal Polyp
    The Antrochoanal Polyp is a benign lesion that derives from a lining of the maxillary sinus. Research shows that it makes up to 6% of all cases of nasal polyps. As it grows, it fills the sinus cavity and continues to rise through the canal further into the nasal cavity and pharynx. The main symptom is unilateral nose congestion (the patient can breathe only through one of the nostrils). Also, patients report repeated episodes of Sinusitis.
    As mentioned above, the condition is benign, but a definitive diagnosis can be made only after pathological verification. The treatment is surgical. Rarely, the disease may mimic or even turn out to be a malignancy (rarely only!). In an ENT examination, it is indistinguishable from other forms of sinonasal polyps. Nasal endoscopy is the most common surgical approach. In the past, avulsion (pulling it out with a special instrument) was the method of choice, but research showed a high rate of recurrence and other associated complications.
  • Ethmoidal Polyposis
    Ethmoidal polyps are pearly white, grape-like masses that grow in both ethmoidal sinuses (air cells) simultaneously (bilateral growth). Unlike antrochoanal polyp that typically appears only in one of the maxillary sinuses as a single formation, ethmoidal polyps grow in large numbers.
    Patients with ethmoidal polyposis often report with allergies and frequent episodes of Sinusitis. The main symptom is a bilateral nasal obstruction (the patient cannot breathe through the nose at all). Unlike antrochoanal polyp which is a relatively rare finding, ethmoidal polyposis is quite common.
    Patients with ethmoidal polyposis need to be on continuous allergy treatment to keep the condition under control (it is the allergy that triggers a chain of events that lead to the polyposis). For those who respond well to the treatment, a nasal spray is all that they need. However, in some cases, surgery comes into play. The goal of the procedure is to make a single sinus cavity of multiple ethmoidal cells so the nasal spray can reach everywhere in the sinuses, that way reducing the recurrence rate of polyps. Yet, the recurrence rate after surgery is not negligible but acceptable – approximately 10%.
  • Inverted Papilloma
    Inverted papilloma is a kind of benign tumor that grows downwards (into the underlying supporting tissues). This kind of growth, over time, changes and destroys the tissues which cause numerous problems to the patient. The condition is benign. However, as it grows, the papilloma puts mechanical pressure on the surrounding tissues and disturbs the anatomical relations in the area (this is why doctors refer to it as ‘locally aggressive neoplasm’). Also, in approximately 5% of patients, it is associated with squamous cell carcinoma (a kind of skin tumor with uncertain prognosis).
    No wonder why ENT surgeons insist on a radical resection of it. The problem with the ENT operating field is…it’s tight. The procedure requires careful planning.
    A general recommendation is to include radiotherapy in those with pathologically confirmed squamous cell carcinoma after the resection of the papilloma.
  • Carcinomas
    Luckily, carcinomas in the region of the nose and paranasal sinuses are not common. Most stay entirely silent for months or even years before they cause symptoms that grab the patient’s attention. Typically, first symptoms are due to the mechanical obstruction they make – nose congestion or recurrent sinusitis episodes. Such problems in middle-aged adults without a medical history of sinusitis or allergies are always a cause for comprehensive ENT examination.
    Generally speaking, the treatment for carcinoma is surgical removal. Paranasal sinuses are not an exception. It is crucial to diagnose the disease as soon as possible and remove the tumor before it spreads. Surgery in cases like this is often complicated, with long post-operative recovery and an uncertain prognosis.

Hypertrophied middle and superior turbinates including their pneumatization - concha bullosa

Turbinates are bony structures inside the nasal cavity, which have a function to humidify, filter and warm up the air as we inhale it. They look like bony lumps. The lining that covers them has the same structure as in the rest of the upper respiratory tract – a lot of cells that produce mucus and a lot of cells with cilia that push the mucus towards the back of the nose. Normally, there are three pairs of turbinates – superior, middle and inferior. Some people have four pairs – it’s a rare, but normal finding. Turbinates and spaces between them form nasal passageways.

In some people, the turbinates may be bigger than they are supposed to be – a condition known as hypertrophy. Also, in some people, the turbinates may be enlarged and filled with air – a condition known as concha bullosa.

Research shows that enlarged turbinates most often don’t cause any problems. However, patients with chronic Sinusitis and enlarged turbinates may need to undergo ENT surgery. The assessment requires a comprehensive ENT examination and CT or MRI imaging. If the ENT specialist suggests that the cause of chronic sinusitis are enlarged turbinates (hypertrophy or concha bullosa), the patient should undergo a surgery for quick and lifelong relief.

Many different surgical treatments are available to treat these. The procedure typically doesn’t require general anesthesia, is safe, and never leaves scars (as it is carried out through the nose).


The outside world is full of potentially harmful microorganisms. Protecting the inside of the body against them is a primary function of the immune system. In the region of the mouth and nose lies a structure known as ‘Waldeyer’s Tonsillar Ring.’ The ring consists of six tonsils. It is a part of the system that contains specialized cells and tissues that constantly fight against microorganisms from the air, foods, and fluids.

Adenoids is one of the tonsils. It sits where the nasal cavity blends with the mouth. In some people (typically children), adenoids are hyperreactive and enlarged. The enlargement causes nasal congestion and interferes with sinus drainage. This is why patients with adenoids suffer frequent and severe episodes of sinusitis.

For a long time, it was thought that the condition affects almost exclusively children, but the recent research studies suggest otherwise. In adults with nasal obstruction and chronic sinusitis, enlarged adenoids are a major contributing factor.

The treatment is surgical – safe, effective and quick. Full recovery is expected.

Scarring and Induced Ostium Stenosis from Surgery

Sometimes, previous surgical procedures cause scarring in the areas where sinus canals open up in the nasal cavity. When that happens, the drainage of the sinuses becomes difficult, mucus and microorganisms buildup, providing a perfect environment for sinusitis.

As for the treatment, the re-opening is often performed in the ENT office setting. However, some patients require a surgical revision (a procedure carried out in an operating theatre). The choice is made by the ENT surgeon since the occlusion is sometimes caused by a scar in the lining and sometimes by changed anatomical relations in the deeper tissues.

Other, rare structural abnormalities - Cleft palate, Haller cells, Onodi cells, etc.

  • Cleft palate
    Cleft palate is a birth deformity in which the mouth roof is not entirely formed thereby establishing a (pathological) communication between the nasal cavity and mouth. The deformity makes speech difficult. Sometimes it is combined with a cleft lip. Both deformities can be successfully treated surgically. While more prominent defects are easily visible, the cleft palate can present as a very subtle deformity in the mouth and remain unnoticed for a long time, causing episodes of recurrent sinusitis and other infections of the upper respiratory tract.
  • Haller cells
    Haller cells are a relatively common finding. They are air cells located around the floor of the eye sockets. Whether or not they pose a risk factor for sinusitis is still a matter of academic dispute among ENT specialists. The body of evidence suggests that in some people they can indeed cause headaches, recurrent sinusitis episodes and other infections in the area. However, most often they are asymptomatic and if ‘silent,’ they don’t require treatment.
  • Onodi cells
    Onodi cells are another rare structural abnormality of the paranasal sinuses. The condition occurs when one of the ethmoid cells lie too close to the optic nerve (a nerve that carries impulses from the eyes to the brain for further processing) or internal carotid artery (the blood vessel that supplies the brain). Onodi cells are mostly asymptomatic. Sometimes an infection from the upper respiratory tract spreads, and they become inflamed. In such cases, they may cause blurred vision or even spread the infection further into the brain (intracranial space). The treatment is surgical.
Share on facebook
Share on google
Share on twitter
Share on linkedin
Share on pinterest

Medically reviewed by SinusDoctor,
Dr G V K Chaitanya Rao

Sinusitis Basics

Sinus Self Assessment Test

Answer our simple 22 point Sinus Questionnaire and get an instant evaluation of the seriousness of your Sinus condition

Sinus FAQ's

Join our Newsletter

If you are suffering from sinusitis for a while, book an appointment with SinusDoctor for thorough diagnosis & treatment

Sinus headache treatment | Sinus Doctor

Get relief from Sinus

Join our Newsletter to get latest updates and tips on Sinus

Sinuses can be Chronic

Did you know? 1 in every 8 person suffer from Sinusitis. Sinuses can be chronic and hamper your quality of life. Book an appointment with SinusDoctor and get relief from Sinusitis.

How severe is my Sinusitis? Take the SNOT22 test to assess your Sinusitis