Salivary gland stones (sialolithiasis)

Sialolithiasis is the medical name for stones in the salivary glands, the glands that make saliva. These stones are also called calculi, and they form in the ducts, the tiny tubes that carry saliva into the mouth. It happens in the major salivary glands, which are the parotid, the submandibular, and the sublingual glands, and it's a benign condition: it isn't cancer.

Picture a garden hose with a small pebble stuck inside. That's what a stone does when it blocks a duct: saliva can't get out, the gland swells and hurts, and this typically happens while eating. There's one more piece. As long as saliva keeps moving, it carries bacteria out with it, the way running water rinses a pipe as it goes through. If the flow stops, the bacteria stay put and can infect the gland. That infection has a name: sialadenitis.

About 85% of stones show up in the submandibular gland, and there's a reason for that. Its duct runs up toward the mouth, so saliva has to travel uphill, and on top of that, this saliva is thicker. That's why it tends to sit and pool. It's also more alkaline, which is the opposite of acidic, and that makes it easier for calcium and phosphate salts to precipitate: they stop being dissolved and turn into solid particles, like the white scale that slowly builds up inside a kettle. Those salts are what the stones are made of.