Sinusitis refers to the inflammation of the sinus membranes due to an infection caused by a virus, bacteria, or fungus. The sinuses are air-filled spaces in the skull. Following are the types of sinuses: Frontal sinuses, Maxillary sinuses, Ethmoid sinuses, Sphenoid sinuses. If the opening from a sinus cavity becomes blocked, the flow of mucus gets blocked and results in pressure buildup causing pain and inflammation.