This is not just cold and flu season. It's also sinusitis season.

You can get a sinus infection at any time of the year, but doctors say they see more patients with sinus complaints now because cold, dry air and respiratory bugs set the stage for sinus malfunction.

Unlike the flu, sinus infections rarely kill, but they are still a big deal. According to the U.S. Centers for Disease Control and Prevention, 29 million adults — 11% of the population — were diagnosed with sinusitis in 2018.

Count yourself lucky if you've never had a clogged sinus make it feel as if your head might explode. But it doesn't end there. Sinus malfunction has been associated with sleep, heart and lung problems, said Dr. James Palmer, director of rhinology (sinus surgery) at Penn Medicine.

The sinuses are connected, hollow cavities in the skull that run behind the center of the face, from the forehead to beneath the cheekbones. Connecting the larger sinuses is a labyrinth of smaller sinuses.

Each day, the sinuses produce a quart or more of mucus, which traps bacteria, and, ideally, ushers them out holes that drain into the throat. When mucus gets trapped in a sinus, it provides what Dr. Donald Solomon at Cooper University Hospital called a "warm, happy environment" for bacteria that might normally be swept away.

Typically, sinus infections happen after you've had something else, like a cold or the flu, so you're looking for symptoms that get worse after a couple of weeks. Sinus infection symptoms include thick mucus, pressure pain over an inflamed sinus, pressure in upper molars, ear fullness, postnasal drip, sore throat and coughing that's worse at night. Headaches, fatigue and fever can also be present.

Ibuprofen or acetaminophen can reduce sinus pain. Doctors might prescribe a short course of antibiotics. Whether oral steroids should be used for sinusitis is controversial.