Your sinuses are air-filled spaces inside your forehead, cheekbones, and behind the bridge of your nose. When they get inflamed — usually because of an allergic reaction or an infection — they swell, make more mucus, and the channels that drain them can get blocked.
The build-up of pressure in your sinuses causes pain that feels like a headache. You’ll feel a deep and constant pain in your cheekbones, forehead, or the bridge of your nose.