Sinusitis is often caused by bacteria and requires antibiotics for treatment. Sinusitis can also be caused by viruses (meaning antibiotics would not help). Upper respiratory infections and colds are viral illnesses. Proper diagnosis of these potentially similar conditions prevents confusion as to which medications should be given. Overtreating viral infections with antibiotics can be dangerous.

Another noninvasive diagnostic tool is ultrasound. The procedure is fast, reliable, and less expensive than a CT scan although the results are not as detailed. Ultrasound has not been widely accepted for diagnosis of sinus infection by the medical community, especially among ear, nose, and throat physicians (ENTs, also known as otorhinolaryngologists). This is partly because a CT scan offers the ENT physician a more detailed image of the anatomy, which helps plan possible surgery.

If symptoms persist despite adequate therapy, a referral to an ENT (ear, nose, and throat) physician may be made.

In addition to specializing in sinusitis, the ENT physician can directly visualize the nasal passages and the connection to the sinuses with a nasopharyngoscope, or sino-nasal endoscope. This is a fiberoptic, flexible or rigid tube that is inserted through the nose and enables the doctor to view the passageways and see if the sinuses are open and draining correctly.

Anatomical causes of breathing difficulties may also be found, such as a deviated nasal septum, nasal polyps, and enlarged adenoid and tonsils.

An ENT specialist may also drain the affected sinus to test for organisms. This is a more invasive test. During this procedure, a doctor inserts a needle into the sinus through skin (or gum) and bone in an attempt to withdraw fluid, which can be sent to the lab for culture. Any present bacteria can be identified, usually in less than two days.

Antibiotics may be given for treatment. If necessary, discomfort is alleviated by local anesthesia. The draining procedure is seldom used, because the CT scan may suffice for the diagnosis of sinusitis, and standard antibiotics are usually effective even when the exact bacterial cause is not known.

Home care can help open the sinuses and alleviate their dryness.

Inhale steam two to four times per day by leaning over a bowl of hot water (not while the water is on the stove) or using a steam vaporizer. Inhale the steam for about 10 minutes. Taking a hot, steamy shower may also work. Mentholated preparations, such as Vicks Vapo-Rub, can be added to the water or vaporizer to aid in opening the passageways.