Salivary stones are buildups of crystallized saliva deposits. They are the most common cause of swollen salivary glands. Sometimes salivary stones can block the flow of saliva. When saliva can't exit through the ducts, it backs up into the gland, causing pain and swelling. Pain is usually off and on, is felt in one gland, and gets progressively worse. Unless the blockage is cleared, the gland is likely to become infected.