13 Sneaky Causes of Sinus Infections

Sinus infections, the cause of untold misery, strike about 37 million people in the U.S. each year.

On the surface of things, the cause of sinus trouble is clear. Teeny holes that connect your nasal passages to your sinuses (basically a collection of hollow, moist cavities that lurk beneath your nose, eyes, and cheeks) get blocked. Then gunk builds up in your sinuses, germs may grow, and you feel, well, hideous.

But the cause of the blockage is sometimes trickier to figure out. Here are 13 things that can cause an acute sinus infection (the most common type) and, in some cases, lead to a chronic sinus infection.

RELATED: 10 Signs You Could Have a Sinus Infection

Most sinus infections start with a cold. Colds are caused by a virus, which can make nasal tissue swell, blocking the holes that normally drain sinuses.

If your sinus infection, also called sinusitis, is caused by a virus, antibiotics won’t help since these drugs kill only bacteria. Your symptoms will probably get better after about a week or so. A decongestant can help, but don’t use it for more than four or five days to avoid becoming dependent.

The best defenses against these sinus infections are the same things that protect against colds and the flu. In other words, get a flu shot, wash your hands, and don’t chill with the visibly ill.

RELATED: 11 Signs It's More Serious Than the Common Cold

Because inflammation can block the nasal passages and prevent draining, allergies are often associated with sinus infections. In fact, studies have shown that people with sinus infections who have allergies tend to have more extensive sinusitis, says Sonia Bains, MD, assistant professor in the Division of Pulmonary, Critical Care, Allergy, and Sleep Medicine at the Medical University of South Carolina.

If you’re prone to allergies or hay fever, avoid things that trigger allergic reactions, such as dust mites, pet dander, mold, and cockroaches. Prescription or over-the-counter antihistamines and prescription nasal sprays can reduce chronic inflammation in the sinuses and nasal lining.

RELATED: 7 Signs You Have Allergies—and Not Just a Cold

If a cold does not resolve in 10 to 15 days, bacteria may have joined the party.

Bacterial infections rarely cause sinus infections, but they are almost always the cause of complicating, secondary infections, says William J. Hueston, MD, professor and chair of the Department of Family Medicine at the Medical University of South Carolina, in Charleston. In these cases, it's most likely Streptococcus pneumoniae or Haemophilus influenzae.

These bacteria lurk in healthy people; they’re waiting for the right circumstances to grow. Take a decongestant during a cold to avoid those circumstances. If you do develop bacterial sinusitis, you can treat it with antibiotics.

RELATED: What You Need to Know About Viral vs. Bacterial Pneumonia

Nasal polyps are small, benign growths that develop from nose or sinus tissues and can cause the sinus cavities to become blocked, preventing mucus from draining and causing sinus infection. These little gems can also restrict airway passages, which can in turn trigger headaches.

Chronic allergies can cause long-term swollen and scarred areas of the nasal passages and polyps, according to Dr. Hueston. People with nasal polyps often have a decreased sense of smell.

Polyps are treated with nasal steroid sprays or a short course of oral steroids, and if steroid treatments don’t work, surgery may be necessary.

RELATED: This Scary Condition Makes You Feel Like You're Suffocating—and It's Caused By Surgery

Allergens and pollutants in the air—like dust, outdoor air pollution, and strong odors like perfume—may contribute to coughing, irritate your nose, and cause inflammation that can increase your risk of sinusitis, according to Dr. Bains.

Avoid these irritants as much as possible to reduce the occurrence of sinus infections, particularly if you suffer from allergies or asthma. An air purifier may also reduce pollutants in the air.

If you’re prone to sinus infections or congestion, avoid spending long periods in chlorinated pools, as chlorine can irritate your nasal lining and sinuses.

Diving into water can be a problem too. The pressure during a dive can push water into your sinuses and irritate and inflame the tissue.

RELATED: 11 Reasons You Have a Stuffy Nose–and What to Do About It

Travel a lot for work or pleasure? It could aggravate your sinuses.

When the air pressure is reduced in-flight, it can cause pressure to build up in your head, which in turn can block your sinuses and air passages and aggravate cold symptoms. This is particularly problematic during takeoff and landing.

If you’re congested or suffer from frequent sinus infections but can’t miss your flight, use a decongestant nasal drop or inhaler before takeoff to keep your sinuses clear.

RELATED: 10 Products to Help You Find Sinus Relief

"Fungi are very unusual causes of sinus infections," says Dr. Hueston. While fungal sinus infections can occur in healthy individuals, they are most common in people with weakened immune systems.

When your immune system is vulnerable, fungi can grow, especially in damp and dark environments—aka your sinuses. The most common fungus associated with sinusitis is Aspergillus.

In some people, chronic sinusitis can be caused by an allergic reaction to a fungus.

Treatments may include surgery to remove the fungi, antifungal therapy, or scraping the infected sinus. See your doctor if you have fever, headache, and vision problems for more than 10 days.

While it’s true that nasal decongestant sprays relieve congestion—they constrict the blood vessels in the nose—you should avoid prolonged use of over-the-counter nasal sprays, as they can make your symptoms worse if not used as directed.

If you use sprays for an extended period of time, you can become less sensitive to their effects so that your nose becomes swollen again, a condition known as rebound nasal congestion, says Dr. Bains.

As a result, prolonged use of OTC nasal sprays can lead to dependency, adds Dr. Hueston, who recommends that people who use sprays to treat cold symptoms stop after four or five days.

Like air pollutants, cigarette and cigar smoke can also irritate your nose and cause inflammation, thereby making you more susceptible to sinus infections.

"People who smoke may be at higher risk [of sinus infections], because their natural sinus-cleaning system is damaged by cigarette smoke," says Dr. Hueston. "So they accumulate more ‘junk’ in the sinuses, which can clog passages when they have a cold."

RELATED: Is It a Cold or Sinus Infection? How to Tell the Difference

When mucus is trapped in the nasal passages for long periods of time, it can lose water and thicken. The result? It worsens symptoms and makes sinusitis more likely.

Therefore, doctors recommend you keep your nose as moist as possible. Start by drinking lots of water and avoiding caffeine, and use a humidifier to keep indoor air moist during the winter.

The occasional use of nasal irrigation treatments, like saline sprays, may also help treat or prevent sinusitis symptoms.

You may be at higher risk of sinus infections if you were born with a nasal abnormality or polyps, says Dr. Hueston.

Narrow drainage passages, tumors, or a cleft palate can block openings in the sinus, preventing mucus drainage.

The mucus can then get infected with viruses or bacteria, says Dr. Bains. A deviated septum—when the center section of the nose is shifted to one side—is often associated with chronic sinus infections, as are enlarged adenoids, tissue masses in the passage between the throat and nasal cavity that trap and destroy germs.

Surgery may be necessary to correct these abnormalities.

Chronic conditions, such as cystic fibrosis and other disorders that weaken your immune system, can lead to inflammation in the airways and make you prone to developing thick mucus.

This thicker mucus, or an impaired ability to fight germs due to diabetes or HIV infection, can set the stage for sinus infections.

To get our top stories delivered to your inbox, sign up for the Healthy Living newsletter