Your sinuses are air-filled spaces in your skull behind your cheeks, eyebrows, and jaw. Sinusitis, or a sinus infection, happens when you have swollen or inflamed tissues within the sinuses. You may know that viruses, bacteria, and fungi are all potential reasons for what causes a sinus infection—but they aren’t the only causes.^1,2

Other causes that contribute to developing a sinus infection include allergies, sinus structure issues like polyps, and lifestyle factors like smoking.¹ Read on to learn more about the causes of sinusitis, risk factors, and when to see a healthcare provider.

1. Viruses

Most sinus infections start with a cold.³ Viruses cause colds and can make nasal tissue swell, blocking the holes that usually drain sinuses.⁴

If a virus causes your sinus infection, antibiotics won’t help since these drugs kill only bacteria. However, you can use treatments to help, such as nasal steroid sprays, oral decongestants, and/or nasal irrigation.²

2. Allergies

Because inflammation can block the nasal passages and prevent draining, allergies are often associated with sinus infections. If you’re prone to allergies or hay fever, avoid things that trigger allergic reactions, such as dust mites, pet dander, and mold. Prescription or over-the-counter antihistamines and nasal sprays can reduce chronic inflammation in the sinuses and nasal lining.⁴

3. Bacteria

While most infectious causes of sinus infections are actually viral, if you do develop bacterial sinusitis, it can be treated with antibiotics after consulting with a healthcare provider.⁴

4. Nasal Polyps

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 growths can also restrict airway passages and trigger headaches.⁵

Polyps are treated with nasal steroid sprays or a short course of oral steroids. If steroid treatments don’t work, surgery may be necessary.⁵

5. Irritating Pollutants and Smoke

Allergens and pollutants in the air—like dust and outdoor air pollution—may play a role in sinusitis development.⁶ Avoid these irritants as much as possible to reduce the occurrence of sinus infections, particularly if you have allergies or asthma. An air purifier may also reduce pollutants in the air.⁷

6. Fungi

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 in damp and dark environments like your sinuses. The most common fungus associated with sinusitis is Aspergillus.⁸

Fungal sinus infections range widely from mildly irritating to extremely severe and potentially fatal. Treatment will also vary widely depending on what type of fungus is involved and whether the infection is acute or chronic.⁸

7. Nasal Anatomy

Structural problems related to your nose can block openings in the sinus, preventing mucus drainage. For example, a deviated septum—when the center section of the nose is shifted to one side—and enlarged adenoids, tissue masses in your airway, are also often associated with chronic sinus infections. Surgery may be necessary to correct these abnormalities.

However, complications of repeated sinus surgery, such as scar tissue formation, can actually become a cause of chronic sinusitis.⁹¹

Risk Factors

A few factors can increase your risk of developing sinus infections. They include:^2,1,3

• Altitude changes, like during flights or scuba diving
• Diseases, such as cystic fibrosis, that prevent proper use of cilia, little hair-like structures in the respiratory tract
• Large adenoids—lymph tissues found in a person’s airway
• Overuse of decongestant nasal sprays
• Recurrent viral colds
• Seasonal allergies
• Sinus-related structure problems, like nasal polyps
• Smoking or secondhand smoke exposure
• Weakened immune system or immune system-suppressing medication use
• Swimming or diving in chlorine
• Dental infection or disease

When To Contact a Healthcare Provider

A healthcare provider can determine if you have a sinus infection with a physical examination and getting information about your symptoms. Also, seek medical attention if you:³

• Develop a sinus infection many times during the year
• Have a low-grade fever (less than 101 degrees) that lasts longer than one or two days
• Have a fever of 101 degrees or more
• Have severe symptoms like a very bad headache or pain in your face
• Have symptoms that improve but then get worse
• Still have symptoms after 12 weeks or have symptoms that don’t get better after 10 days

A Quick Review

Sinusitis has several causes, from germs like viruses and bacteria to nose structure issues. Many risk factors can contribute to a sinus infection, such as nasal obstruction due to polyps or a deviated septum, allergies, or a weakened immune system. See a healthcare provider if you experience things like multiple sinus infections in a year, severe sinus infection symptoms, or long-lasting symptoms.

Sources:

1. MedlinePlus. Sinusitis.
2. American Academy of Family Physicians. Sinusitis.
3. Centers for Disease Control and Prevention. Sinus infection (sinusitis).
4. American College of Allergy, Asthma, and Immunology. Sinus infection.
5. MedlinePlus. Nasal polyps.
6. Battisti AS, Modi P, Pangia J. Sinusitis. In:StatPearls. StatPearls Publishing; 2023.
7. U.S. Environmental Protection Agency. Air cleaners and air filters in the home.
8. Akhondi H, Woldermariam B, Rajasurya. Fungal sinusitis. In:StatPearls. StatPearls Publishing; 2023.
9. Cappello ZJ, Minutello K, Dublin AB. Anatomy, head and neck, nose paranasal sinuses. In:StatPearls. StatPearls Publishing; 2023.

Important Notice: This article was originally published at www.health.com by Kristin Koch where all credits are due. Fact checked by Karis Cho, MD