**Sinusitis, or a sinus infection, is a common medical condition that affects 10 million to 15 million people each year, notes the Merck Manual Home Health Handbook 12. Characterized by pain or pressure between the eyes and around the forehead and nose, the condition can last weeks or months. While most infections disappear on their own, in severe cases, a sinus infection can cause life-threatening disease and vision loss, warns Dr. Jay M. Dutton of the American Rhinologic Society 26.

Causes

A sinus infection occurs when sinuses -- empty cavities behind your cheeks, nose and around your eyes -- become swollen, preventing mucus from properly draining into the nasal passages, according to the Centers for Disease Control and Prevention 2. A bacterial infection from an upper respiratory tract infection, which often begins as a cold, is the most frequent cause of a sinus infection 2. Other causes include allergies, fungal infections, pollutants and a blockage or abnormality in the nasal passage.

Types

There are four types of sinusitis — acute, sub-acute, chronic or recurrent 4. Acute sinusitis may last up to four weeks, while sub-acute may last four to 12 weeks and chronic may last three months or longer, according to MedlinePlus 34. Three or more episodes of a sinus infection every year is known as recurrent sinusitis, the American Academy of Allergy Asthma and Immunology adds 25.

Symptoms

**An infection in the sinuses between the eyes and on either side of the nasal cavity, results in pain behind and between the eyes, a telltale sign of sinusitis, the Merck Manual Home Health Handbook notes 12. Accompanying this pain is often tearing and a headache over the forehead. Similarly, an infection of the sinuses in the cheekbones can also cause pain just below the eyes as well as a headache and toothache 2.

Treatment

Various medical options are available to treat a sinus infection, depending on its cause and severity 2. Your doctor may prescribe a decongestant to help drain the sinuses and relieve pressure, a mucus-thinning medication, or a steroid nasal spray to reduce swelling to open the nasal passages, the American Academy of Allergy Asthma and Immunology notes 5. If you are suffering from severe swelling around your eyes, your doctor may prescribe an antibiotic. Other treatments include an antifungal medicine, or surgery if a nasal abnormality is the cause.

Prevention

Avoid contact with people suffering from a cold and wash hands frequently to reduce your chances of developing an upper respiratory tract infection 2. Maintain a diet rich in fruits and vegetables to boost your immune system and drink plenty of fluids. Avoid smoke and pollutants, and use a humidifier to keep air moist.

Complications

An infection of the sinuses above or below and between and behind the eyes can cause the infection to spread to the eye, resulting in complications ranging from swelling of the eyelid and an infection of the tissue surrounding the eye, to vision loss and even blindness, note MayoClinic.com and the American Rhinologic Society 246.