What Is a Sinus Infection? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Lying behind your eyebrows, behind your cheekbones, and between your eyes are your sinuses — air-filled cavities lined with a mucous membrane that filters and humidifies the air you inhale.

This membrane produces and circulates mucus into your sinus and nasal passages to help remove dust, particles, and microbes from the air that you breathe. Tiny hair-like cells called cilia sweep the mucus to the openings that lead to the back of your throat, allowing it to slide down into your stomach. (1,2)

A sinus infection occurs when the sinuses (or, more specifically, the mucous membranes) become inflamed and swell up because of a viral, bacterial, or fungal infection. The infection can be acute or chronic (long-lasting). (3)

The hallmark symptoms of a sinus infection, whether acute or chronic, are:

Nasal congestion (stuffy nose)
Thick nasal discharge that is yellow to green in color
Decreased or lost sense of smell
A feeling of pain, pressure, or fullness in the sinuses (1)

The terms “sinus infection” and “sinusitis” are often used interchangeably, but sinusitis simply refers to the inflammation of the sinuses, with or without an infection. The medical term for sinusitis is rhinosinusitis (“rhino” meaning “nose”) because the illness affects the mucous membranes in both the sinuses and nose. (3,4)

Sinus infections ultimately develop because of sinus and nasal blockages that result in sinus inflammation. There are several underlying causes of sinus blockage, including various environmental, anatomical, and genetic factors. But the most common cause of the blockage is inflammation or swelling of the nasal passages because of the common cold or allergies.

In healthy people, mucosal secretions are always moving and draining into the nasal cavity. But when blockage occurs, mucus fails to drain properly, increases in thickness, and fills the sinus spaces.

The cilia also slow down their sweeping and cleaning, making it even harder for mucus to drain.

When the mucus is unable to drain, it becomes the perfect medium for microbes to grow out of control and cause an infection. (8)

Common Colds and Sinus Infections

A viral infection associated with the common cold is the most common cause of sinus infections (also known as viral sinusitis, in this case). (9)

This virus may jump to other people, causing a cold that may also develop into viral sinusitis. (11)

In only 0.5 to 2 percent of cases do people develop bacterial sinusitis (a sinus infection caused by bacteria), which is typically a complication of viral sinusitis. Bacterial sinusitis is not contagious. (9)

In some cases, fungi can cause a sinus infection, particularly if a person has a fungal allergy. But invasive fungal sinusitis generally does not affect people with healthy immune systems. (17)

Top Causes of Sinus Inflammation, Swelling, and Stuffiness

There are numerous causes of sinus blockage and inflammation, which can make sinus infections more likely.

These include:

Allergies
Nasal polyps (abnormal growths inside the nose)
Deviated nasal septum (a bending of the wall between the two nostrils)
Weakened immune system, such as from HIV/AIDS
Facial fractures (from trauma) that restrict the nasal passages
Congenital diseases, such as cystic fibrosis
Asthma and other reactive diseases (4,5)

Types of Chronic Sinusitis or Chronic Sinus Infections

While acute sinusitis often involves an infection, chronic sinusitis does not. Sometimes, the long-term illness is caused by an infection that hasn’t cleared up properly, but most often the exact cause of chronic sinusitis isn’t known. (4)

But clinicians may categorize chronic sinusitis into one of three types depending on the features present.

The most common type of the illness, chronic sinusitis without nasal polyposis, involves swelling and inflammation of the mucous membranes by various non-polyp factors, such as allergies or irritation (from airborne allergens and toxins) and infections.

Chronic sinusitis with nasal polyposis, on the other hand, involves nasal polyps that are large enough to clog the sinus. It’s not always clear why some people develop these polyps and others don’t.

In chronic sinusitis with fungal allergy, people experience a strong allergic reaction to fungi in the air, which causes their mucous membranes to produce a thick, dense mucus. (17)

Risk Factors for Chronic Sinusitis and Recurring Sinus Infections

Whatever the type, several factors can increase a person’s risk of developing chronic sinusitis or make the symptoms worse, including:

Allergies
Exposure to tobacco smoke or other airborne irritants
Immune system disorders
Viral infections (including the common cold)
Intolerance to aspirin
Deviated nasal septum (4,17)

To diagnose if you have a sinus infection, your doctor will ask about your symptoms and their timeframe, and give you a physical exam. (1,4)

This exam may include looking in the nose for signs of polyps, conducting a transillumination test (shining a light against the sinuses) to identify inflammation, and tapping the sinus area to detect infections. (14)

If you have a chronic sinus infection, your doctor may conduct additional tests, including:

Rhinoscopy or nasal endoscopy to inspect your sinuses and see if your membranes are inflamed
Mucus cultures to determine what is specifically causing your infection (if it has not improved after antibiotics)
Allergy tests to determine what allergens may be triggering your chronic or recurrent infections
CT scan to identify sinus abnormalities, such as polyps or a deviated septum
MRI scan to see if you have a nasal tumor or fungal infection

If you have a serious fungal sinus infection, your doctor may order a bone biopsy to see if the infection has penetrated your bones. (3,4,14,15,16)

Prognosis of Sinus Infection

Most people with acute sinusitis get better without medical attention.

A visit to the doctor is often not required. And since sinus infections are usually related to colds (that is, viruses), antibiotics will not help. (8)

When to See a Doctor About a Sinus Infection

On the other hand, a secondary acute bacterial infection may develop, so it’s advised that you see a doctor if your symptoms last more than 10 days or if your symptoms initially improve but then worsen again within seven days.

See a doctor immediately if you experience:

A persistent fever higher than 102 degrees F (normal sinus infection fevers are at least 100.4 degrees F)
Changes in vision, including double vision
Symptoms that are not relieved with over-the-counter medicines
Multiple infections within the past year
Sudden, severe pain in the face or head
Confusion
Swelling or redness around the eyes
Stiff neck (9,14)

Acute sinusitis causes inflammation and symptoms that often develop quickly and last 7 to 10 days if caused by a viral infection. But the illness can last for up to four weeks if it’s caused by a bacterial infection.

Chronic sinusitis lasts for 12 weeks or more. This inflammation can continue for months or years, and people often describe it as a never-ending cold. (1)

Sinusitis may also be classified as:

Subacute, in which symptoms last from 4 to 12 weeks
Recurrent acute, in which there are at least four acute sinus infection episodes within one year
Acute exacerbation of chronic rhinosinusitis, in which symptoms worsen in a person with chronic sinusitis (5)

But having symptoms of sinusitis doesn’t always mean that you have a sinus infection.

Up to 70 percent of people with acute sinusitis recover without prescribed medications. (15)

Treatment for acute sinus infections focuses on relieving symptoms, such as by:

Drinking lots of fluids and getting plenty of rest
Flushing out the sinuses with a saline nasal wash like a Neti Pot or a saline nasal spray
Inhaling steam several times a day
Using a humidifier
Resting a warmed, moist washcloth or a warm compress over your nose and cheeks (3,13,14,15,16)

Medication Options

Various over-the-counter and prescription medications may help relieve sinus infection symptoms. These include:

Nonprescription pain medications, including acetaminophen (Tylenol) or ibuprofen (Advil)
Corticosteroid nasal spray
Nasal decongestants, which should not be used for more than three consecutive days
Medications to thin secretions to help clear mucus (mucolytics)
Nasal anticholinergic sprays, such as ipratropium bromide (Atrovent), to reduce runny nose symptoms

Antibiotics may be a part of some sinus infection treatment regimes, but only if it is a bacterial sinus infection (and not one caused by a virus or fungus). (3,8,14)

Oral antihistamines may not improve symptoms and can cause side effects. They are not recommended for sinus infections. (8)

Alternative and Complementary Therapies

Some alternative and complementary therapies may help with sinus infection symptoms, such as:

Yoga
Supplements such as the enzyme bromelain
Quercetin, a natural antioxidant found in many foods, including onions, apples, green tea, and red wine

Chronic Sinus Infection Treatment

Chronic sinus infections typically have a more mysterious cause than acute infections — people with chronic sinus infections often require life-long treatment to keep symptoms at bay.

In addition to the options above, treatment for chronic sinus infections may include:

Lifestyle changes, such as quitting smoking and changing home or work conditions to reduce exposure to environmental toxins and allergens, such as dust mites, pet dander, or cockroaches
Oral steroids
Leukotriene modifiers, which reduce inflammation through a different mechanism than steroids
Surgery to reopen sinuses affected by issues like nasal polyps and deviated septum (16,17)

Recent research suggests other treatment options may also exist for chronic sinus infections, including:

Nasal probiotics of the beneficial bacteria lactobacilli (18)
The drug dupilumab, derived from a human antibody, which the Food and Drug Administration (FDA) approved to treat chronic sinus infections with nasal polyps in 2019 (19)
A regime combining oral and intranasal corticosteroid irrigations

Prevention of Sinus Infection

A sinus infection is not exactly contagious. But depending on what caused a person’s inflammation, other people may also develop the illness. For example, the common cold and flu are both contagious conditions that can lead to a sinus infection.

Taking steps to reduce your risk of contracting viral infections can help prevent sinus infections. These include:

Practice good hygiene, such as by washing your hands often and covering your mouth when you cough and sneeze
Get the recommended vaccinations, such as the flu vaccine and pneumococcal vaccine
Keep your distance from people who have upper respiratory infections
Take steps to reduce your stress, which affects your immune system
Keep your immune system healthy, such as by eating a healthy diet rich in fruits and vegetables (14)

Other ways to reduce your risk of getting a sinus infection include:

Don’t smoke cigarettes and try to avoid inhaling secondhand smoke
Minimize your exposure to allergens and pollutants, such as by keeping your home windows closed and using a HEPA air conditioner filter, driving with your external vents closed and air conditioner on, and avoiding activities that expose you to pollen like lawn mowing and leaf blowing
Moisten the air at home with a humidifier and avoid dry environments
Inhale steam or use a saline nasal spray regularly
Drink lots of water
Treat allergies
Irrigate your nasal passages regularly (6,14,16)

Sinus inflammation can spread to the bones and soft tissues of the face and eyes. This can cause:

Cellulitis of the face or around the eyes
Abscesses of the eyes
Blindness

Left untreated, sinus infections can also lead to serious intracranial complications, including blood clots within the cavernous sinus, pus between the skulls and dura mater (cranial membrane), and meningitis. (12)

Each year, acute (short-term) sinusitis affects about 31 million Americans, who spend a whopping $1 billion on over-the-counter medications and $150 million on prescription medications to treat the illness. (3)

Epidemiologic studies suggest 5 to 12 percent of people have chronic sinus infections. However, research published in 2018 suggests this may be an overestimation due to misdiagnosis. According to the study, which relied on imaging tests for diagnosis (rather than symptomatology), about 3.0 to 6.4 percent of people may have chronic sinus infections. (5)

Colds, allergies, and sinus infections can cause similar symptoms, including stuffiness and headache. What’s more, both colds and allergies can cause sinus inflammation. So how can you tell the difference between these illnesses?

The truth is, even doctors can sometimes have difficulty differentiating among colds, allergies, and sinus infections. But the illnesses do present differently.

A hallmark sign that you have a sinus infection is that the illness is, as you’d expect, severely affecting your sinuses. Both colds and allergies can cause congestion and runny nose, but sinus infections typically cause an aching sensation and pressure (feeling of fullness) in the face, including in the ears and teeth.

Additionally, postnasal drip, reduced sense of smell, and halitosis are typically associated with sinus infections.

The mucus associated with a sinus infection is usually green or yellow, though color alone isn’t enough to determine the cause of your nasal distress, as there are many reasons your nasal discharge may not be clear. (6)

Both allergies and colds can cause sneezing, a symptom not typically seen in sinus infections. Allergies never cause fever, which is seen in both colds and sinus infections.

And if your symptoms last more than 10 days, you most likely don’t have a cold. (7)

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