What Is a Sinus Infection?

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A sinus infection, also called sinusitis, is an inflammation of the air cavities in the bones around your nose and eyes, including the paranasal cavities. When drainage sites for the sinuses are blocked, they fill with mucus and you can feel pain and pressure.

Acute sinus infections often start with inflammation from allergies or a viral infection (such as a cold) and sometimes develop into a bacterial infection. Chronic sinus infections are usually due to ongoing inflammation. Structural abnormalities in the sinuses can lead to chronic or recurrent sinusitis. Fungal sinus infections are also seen, especially in people with weakened immune systems.

The Sinuses

The sinuses are hollow recesses in the bones surrounding your eyes, nose, cheeks, and forehead. They include the frontal, maxillary, sphenoid, and ethmoid sinuses. The sinuses are lined with mucous membranes that normally produce fluid (mucus) that helps trap any debris. Hair-like cilia cells line the membranes and sweep along the mucus, which usually drains into the nasal passages and is swallowed throughout the day.

However, when the drainage sites for the sinuses are blocked, the sinuses cannot drain and an infection may develop. The mucus during an infection is thickened by inflammatory cells and changes from watery to thick and clear to yellow or green.

Sinus Infection Symptoms

Sinus infections can be divided into different categories based on how long the infection has been going on.

With acute sinusitis, symptoms are present for less than four weeks. Subacute sinusitis indicates symptoms that are present for more than four but less than 12 weeks.

Symptoms often associated with acute and subacute sinusitis include:

  • Facial pain and pressure over the involved sinus(es)
  • Nasal congestion
  • Colored nasal discharge
  • A decrease in smell and taste sensations
  • Fever
  • A headache
  • Bad breath/bad taste
  • Fatigue
  • A cough
  • Tooth pain
  • Ear pressure/pain

A viral sinus infection tends to improve with each passing day (and without treatment). An acute bacterial sinus infection, on the other hand, is presumed if your symptoms extend past 10 days, get worse after getting better, or are severe.

An acute invasive fungal infection is a rare type that occurs in people with a severely suppressed immune system. The symptoms begin with fever, cough, nosebleed, and headache. They quickly develop eye symptoms (swelling, vision changes) and symptoms of brain involvement.

You are diagnosed with chronic sinusitis when your symptoms are present for 12 weeks or more. 

The symptoms of chronic sinusitis may be mild and must consist of at least two of these:

  • Nasal congestion
  • Postnasal drip or a runny nose with mucus
  • Pain or pressure in the face
  • Decreased sense of smell and taste
  • Chronic cough (in children)

If the chronic sinusitis is due to noninvasive fungal sinusitis (fungal ball), there are few symptoms, which may only include a feeling of fullness, sinus pressure, and some discharge. Chronic invasive fungal sinusitis is mostly seen in immunocompromised patients and it shows the usual symptoms of chronic sinusitis for a long period, but can develop serious symptoms of decreased vision and eye immobility as the infection progresses.

You're considered to have recurrent sinusitis when you have four or more sinus infections in a year.

These sinus infections have the usual symptoms of acute sinusitis and resolve between episodes.

Complications of sinus infection are uncommon, but it is possible for the infection to spread to the tissues around the eyes, skull, or brain. See your doctor immediately if you have symptoms such as a high fever, swelling around the eyes or forehead, confusion, severe headache, or vision changes.


What's at the root of your sinus infection depends on the kind that you have.

Acute or Subacute Sinus Infections

An acute or subacute sinus infection starts with inflammation of the nasal passages due to an irritant, allergy, or infection, such as the common cold. Resulting blockage of the drainage sites of the sinuses is what leads to the development of the infection itself.

Chronic or Recurrent Sinus Infections

Chronic or recurrent sinusitis is usually caused by ongoing inflammation rather than infection. It can develop due to allergic rhinitis, fungal allergies, aspirin-exacerbated respiratory disease (AERD), exposure to irritants (such as cigarette smoke), or repeated viral infections.

Other causes of chronic or recurrent sinus infections include structural abnormalities within the nasal passages and sinuses, such as a deviated septum (the structure that divides the nasal passage into two sides); enlarged adenoids; enlarged turbinates (structures that warm the air in your nose); nasal polyps; and other bony abnormalities that may prevent the sinuses from draining.

Fungal Sinus Infections

A fungal sinus infection can develop either as a non-invasive fungal ball or as an invasive fungal infection that can damage nearby structures . A fungal ball may develop when dead cells and debris from inflammation or an injury accumulate in the sinus and a fungus normally present in the air begins to grow. This can cause further irritation and inflammation.

Invasive fungal infections are more common in people with impaired immune systems.

The types of fungus found are present in the air but don't usually invade the body. They are only able to grow when the body's immune defenses are very low.

Common Risk Factors

Having allergic rhinitis or an upper respiratory tract infection are high on the list of risk factors for acute and chronic sinusitis. You may be more prone to either form of sinusitis if you have structural abnormalities that inhibit sinus drainage.

Problems with low immune function are the biggest factor in predisposing people to fungal sinusitis, but they also increase the risk of various types of viral and bacterial infections. Immunodeficiencies can occur as a result of a genetic problem (such as cystic fibrosis), infection (such as HIV/AIDS), or diseases that affect antibody levels (such as multiple myeloma). Diabetes can also be a risk factor for fungal sinus infections.

Other diseases that can increase the chance for a person to develop sinus infections include gastroesophageal reflux disease (GERD) and non-allergic rhinitis.

sinusitis diagnosis
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A sinus infection is diagnosed based on your symptoms and a physical examination by your healthcare provider. No other tests are usually needed for an uncomplicated acute or subacute sinus infection. If allergies are suspected, you may be referred for allergy testing. If you have recurrent or chronic sinusitis, your doctor may order X-rays or CT imaging to look for the underlying cause.

Microscopic examination and culture of the aspirate from the sinuses can help diagnose fungal or resistant bacterial infections.

In severe cases of sinusitis, especially those that do not respond to the usual medical treatments, you may be referred to an ear-nose-throat (ENT) specialist or otolaryngologist.


The typical acute/subacute viral sinus infection will resolve itself in 10 days or less. You or your child will only need treatment for the symptoms to provide comfort and relief. Saline nasal spray or, for adults, nasal saline irrigation, can help remove the mucus from the nasal passages and sinuses. These remedies can also be helpful for adults with recurrent or chronic sinusitis.

The primary treatment for bacterial sinus infections is a 10- to 14-day course of antibiotics (typically amoxicillin, amoxicillin-clavulanate, or doxycycline).

Chronic sinus infection treatment often includes a nasal steroid spray. In cases of severe inflammation, the use of oral steroids such as prednisone for three to 10 days is often recommended. Other helpful medications include topical or oral decongestants. Antibiotics may or may not be prescribed depending on whether a bacterial infection is present. If so, the therapy may continue for four to six weeks.

Some people require surgery to address a severe sinus infection, especially one complicated by structural problems or nasal polyps. Endoscopic surgery may also be needed for fungal sinus infections.

A Word From Verywell

While a sinus infection may seem like a minor thing to some, it can be quite debilitating while you have it, often distracting you from just about everything but the discomfort it causes. Remember that relief is typically days away. While you wait, taking over-the-counter pain relievers, drinking lots of fluids, getting plenty of rest, using a humidifier, and applying a warm compress to your face can help. And if your symptoms persist for more than 10 days, be sure to speak with your doctor again.

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