The sinuses are a connected system of hollow cavities in the skull. The largest, the maxillary sinuses, are about an inch across and are located in your cheekbones. Your frontal sinuses are located in low-center of your forehead. Your ethmoid sinuses are found between your eyes, while your sphenoid sinuses are located in bones behind your nose.
The sinuses are lined with soft, pink tissue called mucosa. Normally, the sinuses are empty except for a thin layer of mucus. The exact function of sinuses remains unclear.
Experts believe they help humidify the air we breathe in and enhance our voices.
Acute sinusitis develops when the sinuses to become inflamed and swollen, interfering with drainage and causing mucus to build up. A viral infection, such as the common cold, is often the cause; in some cases, a bacterial infection develops.